Service valve (Rotalock)
Also known as: Rotalock valve, compressor service valve, shut-off valve
Short definitionA hand-operated valve on the compressor inlet and outlet and on the liquid outlet of the receiver. It shuts the line, provides a gauge connection and makes it possible to change a component without removing the refrigerant.
The name Rotalock comes from the connection: the valve seats on a threaded stub with a large nut and a Teflon gasket, with no brazing. When a compressor is replaced, only the nuts are undone. The stem has three positions. Fully out, the line is open and the service port closed; this is how the plant runs. Fully in, the line is shut. Turned in one or two turns from fully out, both are open, and that is when the gauge is read.
For maintenance the receiver outlet is closed and the compressor run, so the refrigerant collects in the receiver and condenser; the drier or expansion valve can then be changed easily. A compressor with its discharge side shut is never started, as the pressure becomes dangerous within seconds. Before turning the stem, the packing nut is slackened a quarter turn and tightened again at the end. A valve left without its cap is a well-known source of slow leaks. The gasket is renewed every time the valve is removed.