1. Reduced Pressure Backflow Why they fail

2. 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.

3. 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.

4. 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.

5. 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.

6. Trouble Shooting Flow Chart