Reduced Pressure Backflow

Why they fail

100 PSI 95 PSI 94 PSI

97 PSI

Supply or Inlet Pressure Zone of Reduced

Pressure Relief Valve Outlet Pressure

Reduced Pressure Principle Backflow in normal Flow Conditions both Check Valves Closed

1. Supply pressure of 100 psi pass through check valve #1 which has a minimum of a five pound spring which make the pressure in the zone (red) 95 psi.

2. Supply pressure (blue) travels through the sensing line to the front of the relief valve putting 100 psi on the front of relief valve.

3. Zone pressure (red) goes into the relief valve which has a minimum of a two pound spring making the pressure on the backside of the relief valve 97 psi (yellow).

4. 100 psi front of the relief valve pushes against 97 psi backside relief valve pressure to close the relief valve.

5. Check valve #2 has a one pound spring so the outlet pressure is 94 psi.

RV

Dump

100 PSI 100 PSI

102 PSI

99 PSI

Supply Pressure Trash Zone of

Reduced Pressure

Relief Valve Pressure

Outlet Pressure

Reduce Pressure Principle Backflow in no flow condition with a fouled CV#1

1. Supply pressure of 100 psi passes through check valve #1 which is fouled open, so the pressure in the zone will be the same as the supply pressure 100 psi (blue).

2. Supply pressure (blue) travels through the sensing line to the front of the relief valve show there will be 100 psi on the front of relief valve.

3. Zone pressure (blue) goes into the relief valve which has a minimum of a two pound spring making the pressure on the backside of the relief valve 102 psi (yellow).

4. 100 psi front of the relief valve pushes against 102 psi backside relief valve pressure the relief valve will open and discharge water.

5. Check valve #2 has a one pound spring so the outlet pressure is 99 psi.

100 PSI Backpressure 100 PSI

100 PSI

102 PSI

RV Dump

Supply Pressure Zone of Reduced Pressure

Trash in CV#2

Relief Valve Backpressure

Reduced Principle Backflow Fouled CV #2 under back pressure in a No Flow Condition

1. Backpressure pressure of 100 psi passes through check valve #2 which is fouled open, so the pressure in the zone will be 100 psi (green).

2. Supply pressure (blue) travels through the sensing line to the front of the relief valve show there will be 100 psi on the front of relief valve.

3. Zone pressure (green) goes into the relief valve which has a minimum of a two pound spring making the pressure on the backside of the relief valve 102 psi (yellow).

4. 100 psi front of the relief valve pushes against 102 psi backside relief valve pressure the relief valve will open and discharge water.

100 PSI 95 PSI

97 PSI

RV Dump

94 PSI

Supply Pressure Trash in the Sensing

Line

Zone of Reduced Pressure

Relief Valve Outlet Pressure

Reduce Pressure Principle Backflow with a fouled sensing line

1. Supply pressure of 100 psi pass through check valve #1 which has a minimum of a five pound spring which make the pressure in the zone (red) 95 psi.

2. Supply pressure can’t travel through the sensing line to the front of the relief valve due to trash there will be no pressure on the front of relief valve.

3. Zone pressure (red) goes into the relief valve which has a minimum of a two pound spring making the pressure on the backside of the relief valve 97 psi (yellow).

4. 0 psi front of the relief valve pushes against 97 psi backside relief valve will cause the relief valve to open.

5. Check valve #2 has a one pound spring so the outlet pressure is 94 psi.

Reduced Pressure Backflow Discharging Water from the

Relief Valve

Shut the Outlet Control Valve Off

Check Valve #2 fouled, clean or replace Rubber

Open Test Cock #4 creating a flow Through

the RP

Discharge from Relief Valve Stops YES

Check Valve #1 fouled, clean or replace Rubber

Fouled Relief Valve or Sensing

Line NO

Direction of Flow

Outlet Control Valve

Test Cock #4

Sensing Line

Relief Valve

CV #1 CV #2

Trouble Shooting Flow Chart