User Guide

10
In a suction application, the solenoid valve provides complete isolation for
temperature control and defrosting, or operates as a suction bypass on
installations with two or more evaporators in a series fed by one expansion
valve (see Figure 9).
Suction applications
Note: When used in suction applications, a valve with a low pressure drop should
be used (less than two pounds-per-square-inch differential [psid]). Piston-type pilot
valves often have a minOPD that exceeds this. For this reason, diaphragm valves are
recommended for suction service.
Solenoid valves can be used to “unload” compressors in a variety of ways.
The most common method works as follows:
Stage Description
1 A solenoid is employed to divert discharge pressure to a piston that,
when activated, “blocks” the suction valve in an open position.
2 With the valve blocked open, no compression takes place in
that cylinder.
3 This lack of compression results in a drop in capacity.
Compressor unloading
Solenoid-valve applications (continued)
Suction-Stop Solenoid Valves
Figure 9