The Pressure Reducing Valve
A pressure reducing valve is a device which reduces high pressure cold water from the mains supply to a pressure low enough to stay within the design limits of the low pressure water heater.
Pressure Reducing Valve Principles
These valves work on the following principle:
The force caused by high pressure water acting on a small washer area equals the force caused by low pressure water acting over a large diaphragm area. Based on that, we can assume that the low pressure side of a pressure reducing valve can overcome the high pressure side of the difference in size of the area each acts on.
If we then fit a spring to act in the same direction as the force of the high pressure water and tension it, then the added thrust will open the valve.
By adjusting the tension applied to this spring, we can set the head of water to the required pressure head in the low pressure side of the hot water system.
The photo is of a new Apex 7.6m Pressure Reducing Valve. High pressure water is fed into the valve via the 15mm connection and low pressure water is pushed out of the valve via the 20mm connection. This valve is fully serviceable and has several parts in it which can be replaced if required.
The jumper washer assembly and jet is accessed via the screw cap on the top of the valve. The diaphragm and spring is inside the body of the pressure reducing valve and the valve needs to be taken apart completely to access those parts.
Adjustment to the valve is via the screw at the bottom of the pressure reducing valve – make sure that you undo the lock nut first.
Pressure Reducing Valve Operation
High pressure water enters the 15mm inlet and flows through the valve to fill the hot water system to the set level.
When this set level is reached, the head creates back pressure on the low pressure side of the valve. This pressure acts on the diaphragm, which closes the valve, which shuts off the incoming water flow.
When a hot tap is opened, the set water level falls, reducing the pressure on the diaphragm. Then, less force is pulling the jumper and washer on the valve seat and, aided by the spring, the valve opens.
Now you know all about the pressure reducing valve, check out our article here on simple maintenance you can carry out on your hot water system.
