Tuthill KINNEY 850D, Operator'S Manual

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plugs and any penetrations into the vacuum area and check pump blank off performance before making
permanent repairs with Loctite 515. If gasketed connections are suspected, remake the connections. Plastic
sealing compound may be used to make temporary gaskets; these should not be made too thick since the
material may be squeezed into the pump. Check the shaft seal for mechanical defects, such as a cracked
carbon washer or hardened rubber components.
For checking leaks, a fast acting total pressure gauge used with acetone or a sensitive helium leak detector
can be used. A helium leak detector is the most convenient to use if available.
6.8.1 CHECKING PUMP PERFORMANCE
If the processing time or the ultimate pressure becomes poor with no recent changes in the process or in
system configuration, test the pump to determine if the trouble is in the pump or the connected process
equipment. To check the condition of the pump, measure the blank off pressure as directed below using a
McLeod gauge. If possible, also read the blank off pressure with a thermistor or thermocouple gauge. To
read the blank off pressure, close the pump inlet by means of a vacuum valve or blank off plate.
Connect a vacuum gauge to the suction side and position the gauge tube, facing downward in the higher
area of the manifolding so that the tube will not become flooded and blocked by splashing pump oil. If the
pump is disconnected from the process equipment, connect a 90° elbow, extending upward, to the inlet
flange and bolt the blank off plate, with gauge connection to the open elbow flange.
Operate the pump for a minimum of 15 minutes and record the lowest pressure reached. Average blank off
readings are 5 to 25 microns with a McLeod gauge, and 10 to 100 microns with a thermocouple gauge. The
specification pressure is 10 microns, McLeod gauge reading. If the McLeod gauge reading is low and the
thermocouple gauge reading is high, the pump oil is contaminated, see Oil Contamination. A high reading
of both the McLeod and thermocouple gauges indicates that an air leak is present.
6.8.2 CHECKING PROCESS EQUIPMENT
Attach a vacuum gauge (See the
Installation - Vacuum Gauges
section) to the connection on the system
side of the isolation valve. For this test, the system should be clear of any process work which might give
off vapors and change the reading. Run the pump to obtain the best vacuum possible with the valve open,
then close the valve and observe the pressure rise. If the pressure rise is greater than desired the leaks
should be eliminated. Check the system carefully for loose joints and obvious leaks. Use a leak detector if
available. The trouble can be isolated further by applying the following procedures:
Isolate each segment by valves or blank off plate at convenient locations. Pump down each segment of the
process equipment individually, starting at the segment closest to the vacuum pump.
Check the lowest pressure attainable when each segment is added. If the pressure is close to that obtained
previously, add the next segment. If the pressure is not, leak test the last segment.
When leak-checking process chambers, start at the air and gas inlet valves, doors, sight ports, electrical and
mechanical feedthroughs, gauge tube fittings, and any other gasketed penetrations and O-ring connections.
After a suspected leak has been found, cover it with plastic sealing compound, such as Apiezon Q,or
duxseal and check the equipment performance before sealing the leak permanently. Thus, all permanent
repairs can be made at the same time.
If a leak detector is not available, use the following methods to locate leaks:
1. Cover suspected leaks with a low vapor pressure sealing compound such as Apiezon-Q or duxseal.
Do this while pumping on the equipment and monitoring the pressure. A sudden decrease in pressure
indicates that a leak has been covered. Repair leaks permanently as necessary.
2. If the leak is large, causing pressures less than 1 torr (1.3 mbar), pressurize the process equipment
with 1 PSIG (70 mbar), of clean compressed air and paint a soap solution on suspected leak areas and
bubbles will indicate leaks.
3. If the leak is small causing pressures less than 1 torr (1.3 mbar), use a fast acting medium such as