Maintenance and Service
3-4
To install the jet assembly, proceed as follows.
a
Place the splash baffle in the bottom of the pump. Check that it is located in the outer boiler
groove.
b
Insert the jet base, making sure the ejector is aligned with the foreline, followed by the
remaining stages of the jet. Make sure that all stages are firmly seated and that all drip
shields are in place.
c
Install the cold cap assembly.
3-6
HEATER REPLACEMENT
a
Turn off the power to the diffusion pump and disconnect the power supply.
b
Remove the heater cover and the insulation from the bottom of the diffusion pump.
c
Label the heater wires for proper location during installation.
d
Disconnect the terminal leads.
Use two wrenches when loosening these nuts to prevent
breaking the heater terminals.
e
Remove the nuts holding the heater clamp.
The heater clamp is fairly heavy (eight
pounds); use caution when removing it.
f
Lower the entire heater unit from the pump.
g
Replace the defective heater.
h
Install a new heater crush plate.
i
Assemble the heater, crush plate (with dimples facing the heater element), and clamping
plate as a unit.
k
Coat the boiler studs with an antiseize compound such as FEL-PRO C5A or common milk of
magnesia.
l
Support the heater unit by the clamping plate, line up the holes with the boiler studs, and push
the unit up against the boiler plate. Use two nuts, tightened finger-tight, to hold it in place.
m
Secure the remainder of the nuts finger-tight, then tighten the bolts evenly to a torque of
250 inch-pounds.
o
Replace the heater insulation and the cover.
3-7
ADDING PUMP FLUID
The recommended fluid charge for the VHS-10 and the VHS-400 diffusion pumps is 1000 cc. The
fluid charge will gradually be depleted through use, but the pump will continue to operate normally.
When the charge is reduced to approximately 60 percent of the initial fill amount, the boiler plate
temperature may begin to rise. Under this condition, the thermal switch, when properly connected,
is designed to open the heater circuit.
a
Turn off the power to the pump.
b
Allow the pump to cool until the temperature of the pump body, measured one inch above the
heater skirt, has cooled to 130 degrees F.
c
Vent the pump to atmosphere.
