Trane VAV-SVX02B-EN manual Reversing Relay, Installation and Operation

Reversing Relay

Installation and Operation

Figure 6–Reversing Relay Connections

The reversing relay is a proportional, non-bleeding device for use in pneu- matic control systems where a propor- tional signal from a controlling device must be reversed (see Figure 5).The most common use of the reversing relay is to change the action of a pneumatic thermostat.

Figure 5–Pneumatic Reversing Relay Trane Part No. RLY-755

Output

SBranch

20

(137.9)

B

M Reversing

Relay

S

9 PSI In

(62.06 kPa)

9 PSI Out

(62.06 kPa)

The reversing relay requires three piping connections: main/supply air, input signal air, and output branch air (see Figure 6).The branch line pressure decreases in direct proportion to an increase in the input signal pressure and vice-versa.The input signal is also amplified, thereby minimizing any pneumatic line transmission lag

(see Figure 7).

Input pressure to the relay and output pressure to the PR should always add up to a constant, which is usually set between 16 and 25 psi. For example, with a constant of 18, six-pound input signal will result in a 12 pound branch signal. A bias adjustment screw is provided to retard or advance the out signal.

Input

Branch

Figure 7–Reversing Relay Characteristics

Pressure	Inc.	15
Branch		12
Output		3

3 6 15

Inc.

Input Pressure Signal

4 VAV-SVX02B-EN