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2A2. Insuring circulation. To insure the complete circulation of the drying gas throughout the instrument, an internal circulating pipe is led to the lower end of a reduced tube section and, if practicable, to the extreme top of the instrument. Circulation of gas is upward through this pipe, which discharges upward, and then downward through the optical tube or tubes and the space between the optical tube or tubes and the external casing of the periscope. If the optical tube is made practically airtight, the circulation of gas is upward through the interior of the optical tube, discharging upward against the head window, then downward through the space between the optical tube or tubes and the external casing. A combination of these two methods may be used.

In cases in which the circulation of gas in the interior of the optical tube and between the optical tube and the external casing are in the same direction, suitably placed and fitted diaphragms or bearing collars are provided between the optical tube and the external casing at such points and in such manner that the drying gas is forced to circulate through the space between each successive pair of optical surfaces. Provisions are made to insure that there are no dead pockets in the interior of the instrument through which, the drying gas is not forced to circulate.

Diaphragms installed to produce circulation of drying gas are secured in the manner specified for securing bearing collars. The openings which permit circulation of the drying gas through each closed space in the interior of the periscope are of such dimensions that there is no danger of collapse of the optics, or structure forming the closed space, because of the admission of the drying gas

2A3. Circulation arrangements. Special care is taken in making arrangements for causing circulation of the drying gas to prevent undue difficulties and complications in the method of assembling and disassembling the periscope, and for cleaning, overhauling, renewing, and adjusting the optics and internal mechanisms.

2A4. Inlet and outlet plugs. A drying inlet plug and a drying outlet plug are located in the eyepiece box casting below the hoisting yoke. No other drying inlet or outlet plugs are provided. The preferred location of these plugs is on the side of the tube approximately diametrically opposite the eyepiece. These plugs are as specified in Bureau of Ships Plan No. 549601, Standard drying plug. A suitable lead washer is installed between each plug and its seat. The word inlet or outlet, as appropriate, is legibly stamped or cut in the external casing of the periscope in the immediate vicinity of each drying plug.

2A5. Drying gas. Nitrogen gas in accordance with Navy Department Specifications 51N3b dated 1 November 1941 (abstracted below), is used as the drying gas. Special care is taken to insure that the nitrogen used is free from moisture and from dust or other foreign matter.

Abstract from Navy Department Specifications 51N3b, 1 November 1941, Superseding 51N3a, 2 January 1929; Nitrogen For Use In Optical Instruments; and Cylinders Therefor:

1. a) Applicable specifications:

A-1. The following Navy Department specifications, of the issue in effect on date of invitation for bids, form a part of this specification, and bidders and contractors should provide themselves with the necessary copies:

General Specifications for Inspection of Material 51C31, -Cylinders, Compressed-Gas, ICC3A

2. b) Grade:

B-1 Nitrogen covered by this specification shall be of but one grade.

3. d) General requirements:

D-1. See Section E.

4. e) Detail requirements:

E-1. The nitrogen shall be at least 99.5 percent pure and free from acid, dust, and objectional impurities.

E-2. Cylinders: Nitrogen shall be shipped in cylinders which, unless otherwise specified in the contract or order will be furnished by the Government, and which will conform to Navy Department Specification 51C31, listed in Section A.

E-3. Marking: The cylinders charged with nitrogen shall be painted around the neck with two light gray bands, 3 inches wide, separated by a black band 2 inches wide. The remainder of the body of the cylinder shall be painted black. In addition, each cylinder shall be stencilled on the painted band with the notation Special for use in optical instruments. Painted bands and stencilled notation shall be clear and distinct at time of delivery.

E-4. When Government-owned cylinders are not furnished, the contractor shall furnish cylinders conforming to the latest issue of Interstate Commerce Commission Specification 3-A. The valve outlet shall be male and threaded with national form left-hand threads. There shall be

E-5. Cylinders furnished by the contractor or supplied by the Government shall be rated at 1,800 pounds normal pressure, and at this pressure shall contain approximately 184 cubic feet of gas at atmospheric pressure.

5. f) Methods of sampling, inspection, and tests:

F-1. Volume: A test shall be conducted on each cylinder to determine its volumetric contents as indicated by the pressure of the gas. Each cylinder shall contain not more than 5 percent by volume, in excess of the volume required by the contract or order. The entire volume required by the contract or order shall be considered as the cumulative volume of all cylinders required by the contract or order. Cylinders shall be at normal volume at 1,800 pounds at 70 degrees F, and a lesser volume shall be considered cause for rejection of the cylinders. Compensation for pressure shall be made as provided by Table I (not reproduced here).

F-2. Purity of gas: The gas from one cylinder shall be tested for compliance with the requirements of paragraph E-1.

F-3. Dewpoint: A dewpoint test of bottled nitrogen was taken in the New London Optical Shop. This test showed a dewpoint of -56 degrees centigrade. However, this does not hold true of every bottle, as there may be variance, either plus or minus.

If a periscope is reassembled with moisture in the contained nitrogen-air mixture, no trouble is experienced until the next submerged run. Sea water then cools the tube and optics, moisture is

The most frequent cause of periscope failure in normal service is fogging of the optics resulting from internal moisture. Internal moisture is caused chiefly by leakage of gas past the packing glands of the operating shafts, accompanied by the breathing action of the periscope during temperature changes.

2B2. Kinds of fogging. Fogging of periscopes is caused by condensation of water vapor on the

2B3. External fogging. External fogging can take place on the outside of the eyepiece window or on the outside of the head window whenever the temperature of the glass is below the dewpoint of the air to which it is exposed. Temporary fogging of the outside of the eyepiece window may occur as a result of moisture in the observer's breath, or when the periscope is first raised after being housed in the cold periscope well over a long period of time when the air in the submarine is particularly humid. The condensation that forms on the outside of the eyepiece under these conditions can be wiped off with lens paper. Continuation of this fogging ceases as the instrument becomes warmer.

External fogging of the outside of the head window rarely occurs, but is possible when the temperature of the sea water is appreciably lower than the dewpoint of the outside air. This kind of fogging can be recognized by the fact that when the periscope is first raised clear of the water and the outside surface of the window is still wet, there is no apparent fog, but as the surface dries, condensation slowly appears. This condensation can be rapidly eliminated by occasionally lowering the periscope and wetting the window.

2B4. Internal fogging. Internal fogging is caused by the presence, within the periscope, of water vapor which condenses on one or more optical surfaces whenever the temperature of the optics falls below the dewpoint. Obviously, the most practical remedy for this condition is to reduce the amount of water vapor to a point where condensation cannot take place at the temperatures likely to be met by the periscope in service. This can be accomplished by evacuating the assembled periscope to a low absolute pressure and then recharging it with dry nitrogen.

2B5. Elimination of internal fogging. A new method of servicing periscopes to eliminate internal fogging has been tested and is recommended for adoption by periscope overhauling activities. It should, if possible, be undertaken

As a preliminary step, the periscope should first be tested for tightness with nitrogen under pressure. This obviates the extremely difficult task of locating leaks while the periscope is under vacuum. The periscope is filled slowly, taking 2 hours to build up a pressure of 100 psi gage. Strong gas currents in the periscope should be avoided at all times to prevent the deposit of dust on the optical surfaces; too rapid building up of pressure may derange the optical system. After the pressure has been built up, the instrument is thoroughly checked with soap for leaks. When it has been made tight, the pressure is slowly released over another 2-hour period.

Before evacuating the periscope, the pump should be checked by attaching a mercury manometer to the suction side. The manometer reads in millimeters. It does not begin to register until a vacuum of 29 inches is reached. If the pump is operating properly, it pulls a flat vacuum, that is, the height of the mercury in both legs of the manometer becomes equalized. Care must be taken to keep the pump level to prevent loss of oil from the exhaust port.

Connections are made for evacuating as illustrated in Figures 2-1 and 2-2. All leads should be kept as short as possible. A sealing compound should be used to insure tight joints at the periscope air inlet and outlet valves and at other connections in the evacuating system. It may also be necessary to seal over the inlet and outlet air-valve screws. Sealing compound should not be used on any other part of the instrument.

The periscope is now ready for filling with nitrogen. The nitrogen bottle is connected to the instrument through a silica-gel dryer and filter,

Figure 2-1. Cross-sectional view of air inlet valve body.

or cold trap of acetone-CO₂ mixture. A small amount of nitrogen should be bled to the atmosphere before making final connection at the periscope air inlet to remove any water vapor or dust in the line from the filter. The nitrogen is then slowly introduced, building the pressure up to 8 pounds. Nitrogen should not be taken from a bottle in which the pressure has fallen as low as 400 psi.

The Bureau of Ordnance Mark 3 Mod 0 Instrument Dryer, or the Bureau of Ships nitrogen dryer manufactured by the Navy Yard, Philadelphia, Pa., can be used for drying the nitrogen, provided they are modified. This equipment utilizes silica-gel. Tests have demonstrated that this material is satisfactory for periscope work, provided freshly reactivated gel is used for each

Where silica-gel is used, there is a possibility of introducing particles of the gel into the periscope and it is not possible to check the drying procedure by making a dewpoint test. For these reasons, the method of drying using the acetone-CO₂ (dry ice) mixture should be used wherever dry ice is available.

Figure 2-2. Cross-sectional view of air outlet valve body.

In making connections to the air inlet and air outlet valves on the periscope, the air-valve connection, supplied with the periscope tool and spare parts boxes is utilized.

The Bureau of Ships instructs the manufacturer of periscopes and the building yards to treat each new periscope by a process similar to that just described before installation in new submarines and to attach an appropriate tag to each instrument so treated. Under the following circumstances the Bureau requests that the forces afloat dry and recharge periscopes in service as just described and attach a tag to show date and pressure of recharging:

1. When the internal pressure of any periscope falls to 4 psi or less. If the pressure is found to be between 4 and 7 1/2 psi, it should be increased to 10 psi with nitrogen dried by a silica-gel dryer or by the cold trap method and bled down to 7 1/2 psi.

1. Vacuum gage (Stokes-McLeod Flosdorf Mod. Manometer).

2. Vacuum gage fitting for inlet fitting.

3. Cenco Hyvac Pump.

4. Cenco Hyvac Pump outlet fitting.

5. Pressure gage, 0 to 150 psi.

6. Silica-gel dryer (Figure 2-17). (Note: Silica-gel should not be used where CO₂ is available.)

7. Silica-gel.

8. Reducing valve for nitrogen flask.

10. Thermos jar of pyrex, 2 3/4 inches inside diameter, and 12 inches deep, properly insulated in a metal container having 1/2-inch cork insulation surrounding the flask, and a wax seal covering the joint between insulation and the flask.

11. Copper coil of 3/8-inch tubing, 15 feet long, coiled to 2 1/2 inches outside diameter and inserted in the flask.

11a. Wire screen.

12. Cuno air filter attached in the line between the nitrogen tank and the copper coil. (A filter using a sintered bronze Porex disk may also be used.)

14. Three pounds of CO₂ to fill the flask.

15. Snow Man CO₂ machine.

16. CO₂ Supply (20 bottles).

17. Nitrogen bottle.

Note: In the cold trap method of drying, items 10, 11, 13, 14, 15, 16, and 17 are required and items 6 and 7 are not. If silica-gel drying is used, the reverse is true.

2C2. The Snow Man CO₂ machine. The Snow Man is a small, compact, automatic machine for producing solid carbon dioxide with a temperature of 114 degrees F below zero. From one 50-pound bottle of CO₂ gas, the machine will make about ten 12-ounce solid CO₂ cakes. The machine is operated in the following manner:

1. Lay the bottle of CO₂ on its side and raise the bottom of the tank so that it is about 4 inches higher than the valve end. Connect one end of the copper tubing to the drum and the other to the valve on the side of the Snow Man, using the fiber washers attached to the machine.

2. Before turning on the gas, be sure that the cover of the Snow Man is clamped down tight, and the handle valve is closed. Then open the valve at the CO₂ bottle, and the machine is ready for operation.

3. Open the handle valve just slightly, until the gas is heard going into the machine. Hold this valve open for about 3 minutes or until the safety valve blows. When the safety valve blows, it indicates that the cavity is filled with dry ice. Close the handle valve and raise the cover. The cavity contains a cake of dry ice weighing 12 ounces.

4. Do not open the handle valve wide. Doing so only wastes gas, and does not form a solid cake of dry ice.

5. While the machine is in operation and a cake of dry ice is being formed, do not become alarmed at the escape of gas from the sides and bottom of the machine. This is the excess gas that escapes from the machine during and after the making of each cake of dry ice.

6. After making each cake, clean the opening leading to the safety valve.

2C3. Steps in cycling. Cycling a periscope should be accomplished as follows:

1. If the procedure is carried out on board a submarine, the periscope is first elevated from

Figure 2-4. Periscope elevated.

the periscope well of the submarine to a height sufficient to give the repairman access to the air inlet and outlet connections (Figure 2-4).

2. In no case should the periscope be cycled at a temperature less than 50 degrees F as the partial pressure of the water vapor below this temperature is too low to insure complete drying (Figure 2-5). If the temperature is less than 50 degrees F, the periscope should be removed from the submarine and transported to a convenient building where

cycling can be accomplished and where a temperature above 50 degrees is maintained.

3. Inspect the periscope by observing through it, checking first for external fogging on the head and eyepiece window (Figures 2-6, 2-7, 2-8).

4. Remove the OUTLET PLUG from the AIR OUTLET connection of the periscope (Figure 2-9).

5. On periscopes without a built-in pressure gage, place a 0 to 25 psi or 0 to 50 psi gage in this outlet connection (Figure 2-10).

6. Slowly open the AIR OUTLET valve. A pressure of 5 to 7 1/2 psi is normal, but one

Figure 2-6. Observing through periscope.

between 2 and 5 psi indicates that the periscope should be recharged at the first opportunity. Pressure lower than 2 psi denotes a dangerous condition and may indicate that the periscope is breathing and hence likely to become fogged internally without warning (Figure 2-11). Continued loss of pressure in the periscope, or the excessively free movement of any operating shaft in the eyepiece box, should be cause for an investigation into the tightness of the packing glands. When a periscope is cold, the observer's breath may cause temporary fogging of the outside of the eyepiece window. This condensation can be removed by opening the rayfilter housing

Figure 2-7. External fogging of head window.

and the condition ceases as the instrument becomes warmer.

7. Close the AIR OUTLET valve.

8. Remove the pressure gage from the outlet connection of the periscope (on periscopes without a built-in pressure gage).

9. To remove the stadimeter housing assembly turn the stadimeter handwheel (12) to the observing position, as noted by the stamped numerals located on the stadimeter housing (67

Figure 2-8. Wiping off external fog from eyepiece window.

and 8, Figures 4-24 and 6-8, respectively). The number 58 on the height scale dial (52) should appear approximately opposite the value 2.2 on the range scale dial (50, Figure 4-24). Opposite values of 58 and 2.2 are illustrated in Figure 2-12. In periscopes without the course angle, the number 15 on the height scale dial (13) should appear approximately opposite the value 220 on the range scale dial (14, Figure 6-8). This setting is shown in Figure 2-13. This will make possible

Figure 2-9. Removal of air outlet plug.

Figure 2-10. Insertion of 50 psi gage in outlet connection and opening outlet valve.

the rapid reassembly of the stadimeter housing assembly. Remove the four stadimeter housing bolts (30, Figure 4-24) and then takeoff the stadimeter housing assembly with care to avoid bending the stadimeter transmission shaft (22 and 12, Figures 4-27 and 6-10, respectively). An automatic stop prevents rotation of the stadimeter handwheel (12, Figure 4-24) when not in place.

10. If the periscope requires recycling, remove all the external projection fittings on the eyepiece box, such as the stadimeter housing, training handles, focusing knob, and rayfilter attachment. Access to the packing glands is thus given so that they may be tested for leaks under a 100-psi nitrogen pressure. Testing is preferably done by immersion in water but an application of soapy water may be used.

Figure 2-11. Internal nitrogen pressure ranges for servicing.

11. Release the internal gas pressure, if any, by opening the AIR OUTLET valve.

12. After the internal gas pressure is released, close the AIR OUTLET valve. 13. Remove the INLET PLUG from the AIR INLET connection (Figure 2-14).

14. Insert the hose fitting in the AIR INLET connection of the periscope. Steps 14 and 15 are illustrated in Figure 2-15.

Figure 2-13. Infinity setting of stadimeter dials of Type III periscope.

15. Insert a 0 to 150 psi gage in the AIR OUTLET connection.

16. Open the AIR OUTLET valve (Figure 2-16).

17. The hose pressure from the reducing valve of the nitrogen bottle is reduced from high to low

Figure 2-15. Insertion of nitrogen fitting in inlet connection and pressure gage In outlet connection. Figure 2-16. Opening the air outlet valve with an

Figure 2-16. Opening the air outlet valve with an offset screwdriver.

Figure 2-17. Silica-gel dryer.

pressure so that in filling the periscope a low charging rate may be used.

18. Attach a silica-gel dryer and filter (Figure 2-17) or the cold trap acetone-CO₂ mixture (Figure 2-29) in the line connecting the reduced pressure nitrogen to the AIR INLET connection of the periscope.

Figure 2-19. Series of 4-pound steps during a 2-hour period.

20. Open the AIR INLET valve when the pressure on the charging line is 10 psi, as shown by the pressure gage (Figure 2-18).

21. Fill the periscope slowly, taking 2 hours to build up a pressure of 100 psi in a series of 4-pound steps (Figure 2-19), waiting about 5 minutes between steps. Strong gas currents in the periscope should be avoided at all times to prevent deposits of dust on the optical surfaces; too rapid building up of pressure may derange the optical system.

22. Close the AIR INLET valve when the pressure reaches 100 psi gage (Figure 2-20).

23. Close off the nitrogen pressure at the nitrogen bottle.

Figure 2-20. Closing air inlet valve.

25. Check the periscope thoroughly by means of soapy water (Figures 2-21, 2-22, 2-23, and 2-24), or preferably by immersion in water, and minutely examine it for leaks, particularly through the packing glands. All leaks must be eliminated; otherwise a high vacuum cannot be obtained. The renewal of packing, tightening of packing glands, and gaskets around the head and eyepiece windows must also be checked.

Figure 2-21. Pressure testing outer head and head window with soapy water.

26. When the tightness of the periscope is insured, the pressure is slowly released over another 2-hour period.

27. Close the AIR INLET valve, and remove the pressure gage from the OUTLET connection.

28. Open the AIR OUTLET valve of the periscope to release the pressure as described in Step 26.

Figure 2-23. Pressure testing with soapy water.

30. Connect the mercury manometer fitting to the AIR INLET connection (Figure 2-25).

31. Connect the evacuating fitting into the AIR OUTLET connection.

Figure 2-24. Pressure testing with soapy water.

32. Open the AIR OUTLET valve after the pump has been started, and proceed with evacuation of the periscope. All leads should be short, and with as few joints as possible, to reduce the number of possible leaks.

33. Open the AIR INLET valve so that the line to the mercury manometer gage is free to record the vacuum as the evacuating procedure is carried out.

34. The CENCO HYVAC pump must not be left unattended. If the pump should stop, oil or oil fumes may be sucked into the periscope and deposited on the optics, making necessary a major overhaul of the instrument. If the pump

gives indication of stopping, the hose connection should be promptly kinked (Figure 2-26) and the AIR OUTLET valve closed.

35. Evacuate the periscope until the mercury manometer shows a reading of 4 mm or less (Figure 2-27).

36. When the vacuum has been attained, close the AIR OUTLET valve and secure the pump.

Figure 2-26. Kinking of evacuating hose.

38. Remove the evacuating connection from the AIR OUTLET connection.

39. Close the AIR INLET valve and remove the manometer from the AIR INLET connection.

40. The periscope is now ready for filling with nitrogen. Connect the nitrogen flask, or bottle, to the instrument through a silica-gel dryer and filter (Figure 2-17), or cold trap of acetone and dry ice (Figure 2-29). If the cold trap of acetone and dry ice is used, bleed off a small amount of nitrogen to the atmosphere before making final connection to the periscope AIR INLET connection. This removes any moisture or dust in

Figure 2-27. Mercury manometer reading less than 4 mm.

41. Insert the pressure gage in the AIR OUTLET connection.

42. Open the AIR OUTLET valve to allow free passage of gas to the pressure gage.

43. Connect the nitrogen hose fitting to the AIR INLET connection of the periscope.

44. Open the AIR INLET valve slowly, introducing nitrogen, and slowly build up the pressure to 10 psi.

45. Nitrogen should never be taken from a bottle in which the pressure has fallen to 400 psi (Figure 2-28). Moisture would thus be introduced in the periscope since all nitrogen contains some moisture.

46. Close the AIR INLET valve.

47. Secure the nitrogen pressure.

48. Disconnect the nitrogen INLET fitting from the AIR INLET connection,

49. Insert the INLET plug into the AIR INLET connection.

50. If acetone and dry ice are available, the following method is used for drying nitrogen:

a) Figure 2-29 shows the passage of nitrogen from the nitrogen bottle through a reducing valve into a metal disk filter and into the coil of copper tubing which is immersed in a bath of acetone and dry ice.

b) The dewpoint of the nitrogen passing through the bath is lowered to a temperature of -69 degrees to -74 degrees C. The dewpoint of the nitrogen may be tested as it passes through the cold trap into the periscope, providing an outlet for this test is available.

c) Insert a filter made of metal disks between the nitrogen bottle and the dryer to prevent introduction of dirt, dust, scale, and lint into the periscope. A sintered bronze Porex filter may also be used.

d) In the cold trap, the acetone-CO₂ mixture serves to dry several periscopes if done consecutively. Additional dry ice may be added to keep

51. The dewpoint test should now be made in accordance with the procedure described in Section 2C5. Upon completion of a satisfactory dewpoint test of -50 degrees C or lower, the periscope is bled down very slowly to 7 1/2 psi through the

Figure 2-28. Nitrogen bottle reducing valve gage pressure at 400 psi.

AIR OUTLET valve. Secure the AIR OUTLET valve when the pressure on the mechanical pressure gage registers 7 1/2 psi. (With the built-in pressure gage type, it is only necessary to observe the pressure indicated.)

52. After evacuating and cycling procedure is completed, the AIR INLET and OUTLET plugs and external fittings are assembled in inverse order.

2C4. Dewpoint and testing equipment. Dewpoint is the temperature at which the water vapor in any mixture of a gas and water vapor becomes saturated or condenses. The dewpoint is found by cooling the mixture at a constant pressure until saturation occurs.

The dewpoint test equipment, consisting of a silvered surface on an Erlenmeyer flask in contact with the gas under test, is cooled by immersing the flask in an acetone-CO₂ mixture. As

Figure 2-29. Nitrogen passing through cold trap.

Figure 2-30 shows the equipment necessary to complete the dewpoint test.

1. One centigrade thermometer, range -100 degrees to +50 degrees C.

2. Three 200-ml Erlenmeyer pyrex flasks, with bottom and part of sides silvered, copper-plated, and coated with acetone resisting enamel, or with the internal area silvered and lacquered.

3. 12 inches of glass tubing.

4. Four feet of rubber tubing.

5. Rubber stopper for Erlenmeyer flask.

6. 1/2 lb of CO₂

8. 0.5 liter of acetone.

9. Soft apiezon wax for sealing fittings.

10. Pressure gage, range 0 to 30 psi.

2C5. Steps in taking a dewpoint test. A dewpoint, test should be taken as follows:

1. Heat the Erlenmeyer flasks on a hot plate to drive out all moisture. This is done before assembly with a rubber stopper.

2. Bleed nitrogen from the AIR OUTLET connection of the periscope through rubber tubing connected to the glass tubing of the inlet of the 200-ml flask. Allow an extremely light flow of nitrogen to escape from the glass exhaust tube outlet. This light flow can be noted by placing the outlet tube to a moist lip and feeling the light exhaust flow of nitrogen.

3. Fill the glass beaker with 0.5 liter of liquid acetone.

4. Immerse the Erlenmeyer flask in the acetone in the glass beaker to about 1 inch above the silvered sides and take a temperature measurement

5. Add powdered dry ice and continue to take successive measurements with the thermometer, stirring the acetone-CO₂ mixture.

6. Keep the thermometer raised from the bottom inner surface of the glass beaker (Figure 2-31). A false reading may occur if the thermometer comes in contact with the dry ice.

7. Watch closely for the clouding film on the inner bottom surface of the 200-ml flask (Figure 2-32); the silvered surface on the bottom of the flask aids in detecting this film.

8. When the clouded film of condensed gas vapor is observed, record the temperature. Although a temperature of -50 degrees to -69 degrees C is not likely to be encountered by a submarine in service, having the dewpoint in this range provides a factor of safety and will keep the periscope free from fogging for a longer period if minute leaks should occur.

9. A series of three complete tests is necessary. After each dewpoint test, be sure that the lines and flask are thoroughly dry for each succeeding test.

10. Three Erlenmeyer flasks are used. This provides a dry container for each test, without any loss of time caused by warming and drying.

2C6. Safety precautions for cycling and evacuating periscopes. The following safety precautions should be observed in using the vacuum drying system:

1. Be sure that oil is not introduced into the periscope.

2. Use a reducing valve to lower the pressure of the gas from the tank or bottle.

3. Use dry silica-gel. It should be dried for 2 hours at 500 degrees F and must be of granular form.

4. Be certain that the filter is clean and tight.

5. Check to ascertain that all connections are tight.

6. Bleed out all lines before filling the periscope.

7. Never evacuate a periscope at temperatures less than 50 degrees F.

8. Be sure that the periscope is tight, as all efforts are useless if the periscope leaks.

9. Keep the vacuum pump in a horizontal position and watch carefully to see that the pump

Figure 2-32. Clouding film on inner bottom surface of flask.

does not stop while pulling a vacuum. The pump must always be attended during the evacuating of the periscope.

10. Always take the dewpoint test from the AIR OUTLET connection.

11. Always charge the periscope using a series of 4-pound steps for approximately 2 hours.

12. Never use a nitrogen bottle which has dropped to a pressure as low as 400 psi.

13. Dry out the charging cold trap copper coil after completing every fourth charge.

14. Use apiezon soft vacuum wax around the hose fittings of the AIR INLET and AIR OUTLET connections to insure a complete seal.

15. Dry the Erlenmeyer flasks before each dewpoint test.

2C7. Cleanliness. The greatest care must be taken to avoid introducing dust, dirt, or moisture into the periscope. All apparatus must be kept clean and used for no other purpose. The cold trap and vacuum lines should be blown out before each use with a strong jet from the dry nitrogen flask. Hose lines should be as short as possible and the joints hermetically tight. If periscopes are dried or recharged in place on the vessel, all equipment should be available on board. Long lines for dry gas or vacuum should not be used under any circumstances.

2. When periscopes have been flooded and subsequently emptied of water, the resulting

3. As soon as possible after flooding, flush with fresh water and dry thoroughly, if practicable. Then apply a rust preventive compound similar to Tectyl Grade III or No. 511 to internal parts.

4. If Tectyl is not available, the periscope should be sealed after flushing and left filled with fresh water until repairs are effected.

1. The precautions to be taken when elevating a periscope are:

a) Notify any men working around the vicinity to stand clear.

b) If a cover plate is provided remove the cover plate from the top steady bearing of the submarine.

2. The submarine is moored on either the starboard or port side of the tender (Figure 2-33). Generally it is moored on the side where the periscope is transported most easily to the optical shop.

3. Elevate the periscope to the height required, which should be high enough to accommodate two slings of sufficient length to clear the fragile head (Figure 2-34). Each sling is provided with a spreader bar to prevent contact with the relatively fragile head and taper section of a Type II periscope. The same procedure is followed for other types of periscopes.

4. Secure a suitable forged steel hoisting clamp (2, Figure 2-34) of ample proportion around the outer tube at least 12 inches below the joint between the outer tube and the taper section (Figure 2-24). The hoisting clamp should be lined with asbestos brake lining, or emery cloth placed with the smooth side to the outer tube. Special steel bolts must be used.

5. One or 2 safety clamps (3a Figure 2-34) (the brass clamps supplied with the shipping box will serve) should be secured above the hoisting

6. Place the hook of the lifting crane (4, Figure 2-34) in the hook opening of the spreader bar.

7. Raise the periscope to the observing position and transfer the weight of the periscope to the lifting crane (Figure 2-35). This gives the repairman access to all external parts.

Figure 2-33. Submarine moored on port side of tender.

a) Remove the training handles by taking out eight hinge, bracket bolts (19 and 21, Figures 4-43 and 4-44, respectively), for the left and right training handles of a Type II periscope.

c) Remove the rayfilter by pulling, outward on both spring-actuated plunger knobs (24, Figure 4-40).

d) To remove the stadimeter housing assembly, follow the same procedure stated in Step 9, Section 2B8.

e) Remove the eyepiece attachments that are secured to the anchor screw pins (19, Figure 4-29) projecting from the eyepiece box itself.

Figure 2-37. Rotation of periscope to detect binding.

f) Remove the hoisting yoke when the crane has taken the full weight of the periscope as follows (Figure 7-26):

1) Remove the wire rope with the sleeves for the 7/16-inch wire rope (11) and with the adjusting nuts for the wire rope (10). Lash down the slack wire rope to the wire rope drum of the submarine.

2) Take out the cover ring lockscrews (4).

3) Unscrew the cover ring (2) with a spanner wrench. Remove the hoisting yoke body (1), phosphor-bronze locating collar (9), lower ball bearing race (8), ball bearings and retainer (7), and the upper ball-bearing race (6).

5) Remove the cover ring (2).

9. Slack off the hull stuffing box gland of the submarine before removing the periscope.

10. The periscope must be guided vertically while being hoisted by the crane. Station one man on the fairwater to spot the crane boom directly over the periscope to prevent binding in the steady bearings. Attach a suitable hinged clamp with handles over the outer tube, to rotate the periscope back and forth to observe any tendency toward binding (Figure 2-37). If binding occurs because of the rolling of the tender or the submarine, the hoisting operation should be stopped at once, and resumed only when this condition has been corrected.

11. Hoist the periscope clear of the submarine, and transport it to the upper deck vertically (Figure 2-38). Lower the periscope in the open

Figure 2-38. Hoisting the periscope clear of the submarine to the upper deck of the tender.

clamp cap and clearance wall of the hinge carriage to within 4 inches of the deck. Line the clamp cap and clamp section of the hinge carriage with emery cloth placed with its smooth side against the outer tube. Secure the clamp cap and

12. Carry the lower end of the periscope and the hinge carriage toward the position in which it will lie, in the horizontal position (Figure 2-40), lowering the upper end of the crane. The large wheels of the hinge carriage roll the lower end of the periscope toward its proper horizontal position as the upper end is lowly lowered (Figure 2-41).

13. When the periscope is near the horizontal position, locate the clamp carriage in the proper position, with the upper half of the clamp hinge of the clamp carriage open. Lower the periscope to the lower half of the clamp carriage and close the upper clamp half, securing it with a swinging wing nut (Figure 2-42). The hinge carriage has clearance around the eyepiece box, and is secured to the outer tube just above the coupling, thus carrying the weight of the periscope as it is swung to the horizontal position, and preventing damage to the eyepiece box.

14. Remove the hoisting clamp and the safety clamps (Figure, 2-34).

15. Assemble two horizontal lifting clamps to the periscope outer tube (Figure 2-43) between the, clamp carriage and the hinge carriage. Two 3/4-inch steel bolts, not shown in Figure 2-43, are used on each clamp to fasten the two halves of the clamp together.

16. Roll the periscope by means of the wheels on the clamp carriage and the hinge carriage to the inboard transfer opening of the upper deck (Figure 2-44). Secure the horizontal lifting spreader bar to the plate extension of both horizontal lifting clamps with special bolts 3/4 inch in diameter. (These bolts are not shown in Figure 2-43.)

17. Place the hook of the chain fall of the overhead track in the hook opening in the horizontal lifting spreader bar, and carry the weight of the periscope by the chain hoist (Figure 2-45). Remove the hinge carriage and open the upper half of the clamp carriage.

20. Remove the horizontal lifting spreader bar and the horizontal lifting clamps.

2E2. Installing the periscope. The periscope is installed as follows:

1. Remove the Garlock chevron packing or the emergency flax packing gland assemblies (Figures 2-47 and 2-48) by removing the packing gland nuts.

2. Transport the periscope from the optical shop of the ship to the submarine, following Steps 3 to 20 of Section 2C1 in the inverse order.

4. Replace the suitable hinged clamp with handles (Figure 2-37) over the outer tube, and rotate the periscope back and forth as it is lowered to observe any tendency toward binding. Follow precautions to prevent binding stated in Step 10 of Section 2C1.

5. Hull stuffing box packing. The hull stuffing box gland provides a water seal joint between the hull casting and the outer tube of the periscope. It may be made up of two types of packing: Garlock chevron packing or emergency flax packing assemblies.

a) Figure 2-47 shows the details of the Garlock chevron packing assembly, which consists of the following: upper metal packing ring, one ring of Garlock chevron packing, lantern ring, two rings of Garlock chevron packing, lower metal packing ring, filler ring, and a metal packing gland.

1) Assemble the Garlock chevron packing assembly loosely to determine a measurement from the face of the upper metal packing ring to the inner shoulder face of the metal packing land. Measure the distance from the lower face of the lower steady bearing to the lower face of the extension ring. The difference in the measurements should indicate a 1/16 to 3/32-inch clearance (looseness) between the lower face of the steady bearing and the upper face of the upper metal packing ring after the metal packing gland is brought up hard against its shoulder. To establish the 1/6 to 1/32-inch clearance may require replacing the filler ring, or cutting it down to obtain the desired clearance.

2) Assemble the Garlock chevron packing gland assembly as shown in Figure 2-47. After the metal packing gland is brought up hard against its shoulder, check the clearance around the inner circumference of the packing gland and the outer tube with a .006-inch feeler gage.

3) In view of the temperature zones likely to be met by the submarine, the grease used to pack the lantern ring will vary. For example, in warm climates a heavy grease is required for sealing the lantern ring.

5) It is believed that in cases where leakage occurs with Garlock chevron packing, it can be attributed to a slight off-center condition existing between the periscope and the hull gland, which results in forcing the Garlock packing out of round and opening the seal between the periscope and the packing. Experience has shown that in most cases leakage can be eliminated by the addition of one or two rings of Garlock chevron packing, without any appreciable increase in effort required to train the periscope. Where additional rings of Garlock packing fail to stop leakage, flax packing as shown in Figure 2-48 will stop leakage, but some increase in effort will be necessary to train the periscope.

In taking up the packing gland, use a feeler gage around the periscope to insure equal clearance and proper tightening of the packing gland. This is essential as the shoulder of the packing gland is not brought up against the extension ring.

6. Assemble the azimuth circle and auxiliary circle attachment to the extension ring. Train

the periscope to the forward and after bench marks and check the azimuth circle to read correctly on the lubber's line.

7. After the assembly of the hoisting yoke, fill it with mineral grease Grade II medium. Soft-water pump grease should be added occasionally to the hoisting yoke and the stadimeter housing, chiefly to protect the internal parts from the entrance of water.

8. Raise and lower the periscope while filling the lantern ring area through the external grease fitting of the hull casting with mineral grease Grade II medium.

9. Assemble all external parts in the inverse order.

10. Train the periscope through 360 degrees several times to observe the condition of the steady

Figure 2-48. Emergency flax packing.

bearings and the azimuth circle. Grinding may be noted if chips are left inside the steady bearings, and the azimuth circle is not located properly. When grinding occurs, the outer tube must be smoothed down to remove scratches, and the steady bearings cleaned out and repacked with grease.

11. Check the periscope training handles, altiscope, and power shift to see that they are functioning properly. Check the stadimeter in the observing position, to note that there is no double image at the infinity reading. Check the focusing mechanism to see that the diopter readings are -3 and +1 1/2.

12. After the necessary observations have been made and the periscope is known to be in satisfactory condition, report to the submarine officer, requesting that he inspect the periscope for approval.