7A1. General. The components of the pitometer underwater log that are most likely to
need overhauling are the rotary pump on the
rotary distance transmitter, and the control
unit. The procedure generally followed is to
remove these two units from the ship and
overhaul them in a tender or base shop, in
the manner described previously. The most
practical means of checking the units before
installation in the ship is to operate them
in the shop under the same conditions as those
encountered in service. This entails speeds up
to 10 knots, under water pressures up to 200
psi. The pump should be tested for leakage at
pressures up to 200 psi, and for freeness of
operation, at speeds as low as 1 knot. This
means that the pump should be tight
enough not to leak, yet free enough to operate
at low speeds. The control unit contact arm
must be centered, the contacts and stop rods
properly set, and the unit operated in conjunction with the pump, so that it will regulate
the pump speed down to 1 knot under static
pressures up to 200 psi. Any leakage or binding of the seal assembly will be evident during
this operation.
7A2. Equipment required. The log equipment listed below is the minimum required:
Number of Units
Equipment
Pit. Log No.
1
Pump drive motor, complete
45-3
4
Spacer rods
S645-3
1
Motor mounting bracket (optional)
S686B
1
Motor pump coupling
No number
1
Terminal block
S1144M-1
1
Transtat assembly, complete
21-0
1
Limit switch assembly, 2 switches
S1133-1
1
Follow-up motor with driving pinion
37A
1
Follow-up motor base
K40A-1
1
Transtat mounting plate
S1140-1
1
Gear, 60 T, 24 P
S1134
2
Pinions, 16 T, 24 P
S1135
1
Gear, 72 T, 24 P
S1136
1
Transtat gear, 12 T, 24 P
S1137-1
1
Gear bracket
S1138-1
2
Pivots
S1139
1
Set (2 stacks) armature rectifier
No number
2
Rectifier brackets
S1141
1
Field rectifier
No number
104
1. WATER STORAGE TANK
2. KNOT SCALE
3. STATIC PRESSURE TANK
4. WATER LEVEL GAGES
5. MASTER SPEED INDICATOR
6. ROTARY DISTANCE TRANSMITTER
7. CONTROL UNIT
8. AIR COMPRESSOR LINE (OPTIONAL)
9. DYNAMIC PRESSURE TANK
10. COUNTERWEIGHT
11. AIR LINE TO STATIC PRESSURE TANK
12. PRESSURE GAGE
13. PRESSURE STORAGE TANK
14. VENT LINE
15. HAND PUMP PRESSURE LINE
Figure 7-1. Shop calibration equipment.
105
for properly testing the log. It can be assembled and installed by personnel of tender
and base shops from readily available material. Because the entire rotary distance
transmitter rarely needs to be removed from
the ship for overhaul, for shop use it will be
necessary to provide a duplicate pump drive
motor with the speed control connected to
operate from the control unit.
Any or all of the above parts may be ordered from the Pitometer Log Corporation.
The following hydraulic equipment is necessary: a water storage tank, or water line with
connection, a static pressure tank, a dynamic pressure tank, a pressure storage tank,
a pressure gage, and air compressor, water
level gages, a knot scale, hydraulic hoses, and
fittings and connections. This equipment is
described in the following paragraphs.
7A3. Pump drive motor. The pump drive
motor is the same model as that used on the
ship. It may be mounted on a bench so that
the pumps under test can be easily attached.
If it is desired that the master speed indicator
be tested in the shop in conjunction with the
pump and control unit, the slow speed end of
the motor may be geared in a 6 to 1 ratio to
a self-synchronous transmitter, while the
mileage counter shaft is geared in a ratio of
36 to 1 from the slow speed shaft of the pump
drive motor.
7A4. Transtat and rectifiers. The transtat
assembly and rectifiers may be mounted in an
out-of-the-way place with the three wires
brought out for connection to the control unit.
Power is obtained from 115-volt, 60-cycle a.c.
and is connected to terminals 1 and 3 of the
transtat.
7A5. Knot scale. (See Figure 7-1.) The knot
scale is laid off from the values listed below
and is preferably made of metal. The marks
are cut with a milling machine so that the
distances from the zero line can be measured
accurately. This scale is suitable only for
use with fresh water in tanks and system, and
should be used only for units using the Pitometer rodmeter. Pressure values from rodometers of other manufacturers may differ
from the pressures prescribed here and should
be verified before using this equipment. However, with a correct scale, this equipment may
be used on other types of logs operating on
the principle of pressure differences from a
rodmeter. The scale should be mounted so
that it can be shifted up and own approximately 6 inches. The distances to be marked
above zero, and the corresponding knot speeds
are as follows:
Knot Speed
Distance Above Zero
1
0.58 in.
2
2.32 in.
3
5.22 in.
4
9.29 in.
5
14.52 in.
6
20.88 in.
7
28.42 in.
8
39.17 in.
9
46.98 in.
10
58.00 in.
In any case: distance (inches) equals
0.58 x (knots)2.
7A6. Pressure tanks. (See Figure 7-1.) Two
pressure tanks are mounted one on each side
of the knot scale. The tank on the right side
supplies dynamic water pressure. The left-hand tank supplies static water pressure.
Provision is made for raising and lowering
the right-hand (dynamic) tank, while the
left-hand (static) tank is stationary. When
the dynamic tank is elevated above the static
tank, the head, or difference of level of water,
creates a pressure difference which is equal
to dynamic pressure at some known speed.
Water level gages are mounted in front of
the pressure tanks and show the exact level
of water in each tank. The knot scale mounted
between these pressure tanks is calibrated in
knots, and enables the water level to be read
closely, even at low speeds. The tanks are
made of 3- or 4-inch heavy-duty pipe, approximately 18 inches long with heavy threaded
caps at each end. The glass tubing and gage
fittings should be able to withstand a pressure
of 400 psi for safety. Shut-off cocks should be
mounted on the lower ends, ahead of the
nipples. Nipples only are required at the top.
When mounted as shown in Figure 7-1, the
left-hand (static) tank is connected to the
106
static line. The right-hand (dynamic) tank
is suspended on a chain, or cord, that is connected to a counterweight so that it may be
moved up or down. The tanks should be
mounted so that the zero water level is at
least 3 feet above the control unit bellows
and the rotary pump. However, the shop ceiling may be the determining factor, and may
not permit raising the dynamic tank to the 10-knot mark on the scale. In this case the distance of the zero water level above the bellows will have to be less than 3 feet.
7A7. Water and air connections. (See Figure 7-1.) The hose connecting the dynamic
tank to the lower nipple of the pump must be
long enough to permit the dynamic tank to
be raised to the extreme upper position of
10 knots. The nipples on the upper ends of
the tanks are connected together, and the
hoses are so arranged that they can be connected to a water supply line, or to a water
storage tank, mounted from 8 to 12 feet above
the tanks. It should also be possible to connect these hoses to a pressure line capable of
delivering a pressure of at least 100 pounds
per square inch. A pressure storage tank
mounted as shown in Figure 7-1 permits the
use of higher pressures which are developed
in the top of the tank when water is pumped
up into it from below by a hand pump, or
when air is pumped into the top of it from an
air compressor. An air pressure gage should
be mounted on either the dynamic or static
tanks, on the common air line, or on the pressure storage tank. Connect the left-hand
nipple of the control unit to the center nipple
on the pump; the outer pump nipple to the
bottom of the dynamic tank, and the right-hand nipple of the control unit to the bottom
of the static tank.
7A8. Preparing equipment prior to testing;
Fill both tanks nearly to the top and vent the
control unit and pump thoroughly as described in Section 3A3. Close the left-hand
valve of the control unit, open the bypass
valve, and proceed to center the external contact arm, set contacts, and set the stop rods as
described in Chapter 5. It is advisable to have
at least 3 feet of water above the control unit
while making adjustments. Less head than
this may make it necessary to reset the contacts later.
7A9. Testing equipment at surface pressure.
(See Figures 7-2 and 7-3.) To operate the
units at normal surface pressure, set the
valves and vent cocks of the control unit to
the operating position as shown in Figure
3-3. Vent both the static and dynamic tanks
to the same level at the zero point on the knot
scale. The top connections of the tanks are
open to the atmosphere. Energize the pump
motor power supply. Raise the dynamic tank
to the knot mark desired. If adjusted properly, the control unit should control the pump
speed and cause the transtat arm to regulate,
even at speeds of 1 and 2 knots. Lowering the
dynamic tank to the zero mark should cause
the pump to stop, and the transtat arm to return to the zero voltage position.
7A10. Testing equipment, submerged condition. (See Figure 7-1.) Connect the common
pressure hose at the top of the tanks to a
controllable supply of air pressure, preferably from the pressure storage tank (Figure
Figure 7-2. Pressure tanks at zero position.
107
7-1). Apply air slowly, and test at steps of 50
psi. Because of hose expansion with pressure, the water level in the tanks may change
and the zero of the scale may have to be
slightly lowered. Raise the dynamic tank to
the desired knot mark on the scale and note
the operation of the units. Pressures beyond
200 psi are unnecessary if the parts operate
satisfactorily up to this pressure. The pump
seal bellows should tighten and not leak at
200 psi, while no leakage should be evident at
any part of the control unit. The pump should
not be so tight that it stalls at 1 or 2 knots,
but should be turning over smoothly at 3/4 of
a knot without excess hunting of the transtat
arm. If the test under pressure (submerged
condition) is satisfactory, release the air pressure from the top of the tanks. Do not release
the air by opening the vent cocks on the
Figure 7-3. Dynamic pressure tank of 4-knot position.
control unit. Again test the equipment with only
atmospheric pressure on the water in the
tanks. The units should start and stop freely
as before. However, if the bellows has not
been properly aged as described in Section
5K23, it may be necessary to reset the contacts and stops, and perhaps to recenter the
contact arm. If this has to be done, recheck
for proper operation. When the performance is satisfactory, the equipment under
test may be installed in a ship. It should not
be necessary to make any further adjustments
on the ship.
7A11. Additional tests. An operation test
under at least 100 psi, at 4 or 5 knots, should
be run for 10 to 15 hours if possible. The dynamic tank should be lowered and raised at
intervals during this run to determine whether the units stop and start correctly. When
the pump alone is being repaired, it can be run
at various speeds under pressure to determine whether or not it leaks. However, it will
not be possible to determine whether it is sufficiently free at very low speeds, and it is recommended that it be run in conjunction with
the control unit at these speeds whenever
possible. A static test of 100 to 200 psi of
water pressure may be placed on the control
unit alone to test for leaks; but this shows up
leaks only, it will not test for proper operation under pressure.
7A12. Preparation for pump calibration.
The procedure outlined previously for testing the control unit and pump together, with
a water column as a standard can also be used
to check the accuracy of the log speed and
distance indications. If the control unit contacts have been adjusted as previously outlined, and the pump impeller clearances
maintained, the accuracy of the log should
not be changed from the previous calibration.
However, there are times when an over-all
check for accuracy is desirable. This is particularly true when a new impeller and shaft
or a new thrower disk have been installed in
the pump, causing a possible change in clearances between the impeller blades and the
pump cover. The incorrect setting of contacts on the control unit will cause considerable error at low speeds. If the pump only,
108
but not the entire rotary distance transmitter,
is removed from the ship at this time, it will
be necessary to gear the slow speed end of the
pump drive motor with a 6 to 1 ratio to a self-synchronous transmitter, to transmit rotary
distance to the master speed indicator. The
interior unit of the master speed indicator is
removed from the ship and connected to the
previously mentioned transmitter. The 115-volt supply connected to the 3Y terminals
must be of exactly 60 cycles frequency.
7A13. Pump calibration. The system is
thoroughly vented and is run at speeds of 2,
5, and 10 knots, with atmospheric pressure on
the water in the pressure tanks. There is no
need to check calibration under pressure. To
make a check at 10 knots, for example, the
following operations are performed: Note the
position of the pump orifice plug (Figure 61). Loosen the orifice plate and set it on the
zero percent mark, and tighten the plate retaining screws. Using an accurate stop watch,
time the mileage counter on the master speed
indicator for exactly 1 mile, noting the reading of the speed pointer every 30 seconds. The
time should be close to 360 seconds. Calculate the percentage of error from the
following formula:
(Seconds deviation from 360 x 100)/360 = percent of error
If the time is less than 360 seconds, the
pump is high, or fast. If the time is more
than 360 seconds, the pump is low, or slow.
The true speed reading is more or less than
10 knots by the percentage calculated. Average the speed readings taken above. They
should indicate the same percentage deviation, if any, from 10 knots as was calculated
for the pump. At 10 knots, 0.05 knot is 0.5
percent, 0.1 knot is 1 percent. If the master
speed indicator indications do not agree with
the calculated speed, the error is either due
to the 3Y constant frequency supply not being
exactly 60 cycles, or to the master speed indicator not being in exact calibration. This
test is made primarily to check the pump
accuracy and if the master does not
agree within 0.1 knot, it should be first
checked as described in Section 5M52, before
an attempt is made to change the pointer setting. Using the average speed indication from
above as the standard reference point,
shift the orifice plug to the other marks, plus
and minus 2, 4, and 6 percent. Tighten the orifice plate each time before making a test. It
will not be necessary to time each setting if
the master pointer is read carefully. For example: The speed reading may be 10.05 when
the orifice is on zero, and should be 10.25 for
+2 percent, and 10.45 for +4 percent, and
10.65 for +6 percent. Shift the orifice plug
to the original setting as found on the ship
when the above tests are completed. The error
at zero pump setting should be within plus
or minus 1/2 percent, and within 3/4 percent
at the other points.
If the error is greater than this, it maybe
necessary to re-mark the orifice plate. To remark the place, first file off, or cut off, the
old lines. With the static water level carefully set at zero knots and the dynamic water
level at 10 knots, shift the orifice plug to get
a timed accuracy of plus or minus 2 percent.
Be certain that the orifice plate screws are
tight. This setting will be the new "zero"
point, and a thin line should be described on
the plate opposite the index line of the plug.
Shift the plug to obtain plus and minus marks
of 2, 4, and 6 percent from indications of the
master speed indicator.
Unless the pump error has been found to
be considerable, it will be evident that it is
unnecessary to recalibrate the pump. The
correct registration of speed and distance by
the instrument as installed in the ship and in
actual service is the criterion of the log accuracy. Because so many factors other than
the pump calibration affect the over-all accuracy, it is preferable to attempt to calibrate
the log on a measured mile course as described
in Chapter 6, rather than spend considerable
time on the equipment in the shop. If the
pump and control unit have met the requirements mentioned previously in this chapter,
little trouble may be expected from the log
in actual service.