The controls have snap-acting switches for slow or fast-cycling applications. The one and two-stage models have single-pole, double-throw (SPDT) contact action and the three-stage duplex model has normally closed single-pole, single-throw (SPST) contact action.
A calibrated indicator scale indicates the high setting of the single-stage models. The two-stage models have an indicator for the high setting of the high switch. Duplex models have two indicator scales. These scales indicate the settings at which the single switch and the gang switches activate upon pressure increases.
Figure 1. Terminal switch operation on a pressure increase for SPDT models
On a rise in pressure, the contacts from red (R) to blue (B) open, and simultaneously the contacts from red to yellow (Y) close.