There are three wiring, one is a common, and the needle needle is adjustable. The following pointers are lower limits, and the lower pressure start control relay; the above pointer is the upper limit, the high pressure stop relay, the public line is the utility of high and low voltage control.
The above pointer is the upper limit, the following pointer is the lower limit, the intermediate black pointer indication is the value of the actual pressure. When the actual pressure is on the upper limit, the upper limit is turned on, disconnected from the lower limit. When the actual pressure is between the upper and lower limits, the common end is disconnected from the upper limit and the lower limit. When the actual pressure is under lower limit, the common end is turned on, and the upper limit is disconnected, and the electrical contact pressure gauge is to control the upper and lower limits. The light-free electrical contact pressure gauge is not enough, and there must be an automatic control box of the control pump.
Increase an intermediate relay, 1 high pressure point on the electrical connection pressure table,
Filter Fan Ventilation Filter Fan
one mid point, a low pressure point, current direction: fire line into the midpoint, passing the low pressure point, to the neutral point of the intermediate relay 1 set of contacts, to contact One end of the coil, the other end of the relay coil is connected. Alternatively open contacts on a set of contactors, 2-terminal parallel to the pressure gauge low and midpoint.