three kinds of pressure controls
low pressure high pressure and oil pressure
three kinds of elements
bellows
diaphram
bourdon tube
three kinds of connecting tubes
capillary tube
braided metallic hose
small diameter tubing (1/4 inch)
4 main components of a pressure control
pressure sensing element
connecting tube
electrical switch
adjustment screws
application of pressure controls
used to switch electrical loads such as a compressor motor
and used to operate devices directly such as valves
low pressure control _____ on a rise in pressure
closes
high pressure control______ on a rise in pressure
opens
low ambient control _______ on a rise in pressure
closes
when does oil pressure safety control open
on a rise of differential
describe how a pressure control operates
pressure sensing element moves as a change in pressure is sensed and mechanically opens or closes an electrical switch
what is the control range
the cut in and cut out pressure
what is the cut in
the point where the control makes an electrical circuit
what is the cut out
the point at which the control opens the electrical circuit
what is the differential
the difference between the cut in and cut out pressure
what is a range adjustment
an adjuster that will change both the cut in and cut out point
what are the three applications of a low pressure control
1 used as a safety control - to protect against low charge
2 used as a temperature control - cycles the compressor on saturated refrigerant temp
3 used as a pump down control - shuts down the compressor after a remote thermostat stops liquid flow
what should the cut in and cut out be on a pump down system
cut out as close to 0 psig without entering a vacuum
cut in set to max operating temp converted to psig on PT chart divided in half
describe the steps to set low pressure control
1 install service manifold (gauges)
2 move ssv toward the front seat to reduce pressure on
what is a high pressure controls purpose and what is another name for it
a safety control to protect the compressor and the system when excessive high pressure is sensed
aka pressure limiting device
how does a high pressure control operate
opens on a rise in pressure above the set point
what is the rule of thumb for a high pressure control
air cooled condensers systems set 20% below design test pressure
water cooled systems set 20% above normal condensing pressure
when would you use an oil pressure safety control
on a compressor equipped with an oil pump to protect the compressor from a loss of oil pressure
how long is a time delay on an oil pressure safety control
90-120 seconds
what causes an oil pressure safety control to open
a decrease in net pressure
