Figure 13-9. - Suction throttling valve.

in line with the outlet of the evaporator. This system is designed to limit the amount of low-pressure vapor entering the compressor. The suction throttling valve operates as follows:

1. The outlet pressure enters the valve on the bottom.

2. The gas pressure passes through a fine screen and small bleeder holes to act on a diaphragm.

3. The valve spring and atmospheric pressure oppose the gas pressure on the opposite side of the diaphragm.

4. As the outlet pressure of the evaporator overcomes the opposing forces, the diaphragm and piston move upward, allowing low-pressure gas to flow through the valve and flow to the inlet of the compressor.

As pressure again drops on the inlet side of the valve, atmospheric pressure and valve spring pressure close the valve again. A vacuum power unit is mounted to the top of the valve to help reduce valve spring pressure and prevent icing at high elevations.