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User avatar
By nt2

I need to learn how to adjust the brass pressure reducing valve shown in the two photos, and there appear to be two controls on the device. This feeds cold water to the central heating system.

The first is the black plastic knob which shows C <----> A along an arc. C is in the CW direction, and A is in the ACW direction. Do they mean CW/ACW, or something else, and what does the knob control ?

Similarly what does the brass screw/locknut on the other side adjust ? ... s.jpg?dl=0

Finally is the second valve above the first (on the on the inlet side) a non-return valve ? ... 2.jpg?dl=0

Thank you.
Brass PRV - two adjustments.jpg
Brass PRV - two adjustments.jpg (135.22 KiB) Viewed 4352 times
Brass PRV - valve 2.jpg
Brass PRV - valve 2.jpg (79.94 KiB) Viewed 4352 times
Last edited by nt2 on May 1st, 2020, 8:24 pm, edited 9 times in total.
User avatar
By nt2
This feeds the CH side of a hot water cistern, and the house radiators (see photo). Above the pressure reducing valve and non return valve is an isolating valve that is normally closed. The CH system has an expansion tank beside the boiler to even out pressure.

Over-pressure has possibly contributed to the early failure of the water pump seal, though the pressure was well below the 10 bar rating of the pump. Contaminated water then dripped down to the pump electrics (which should have been rotated to above the pump) and appears to have led to the overheating and melting of one of the internal connections. A new pump arrives today.

The pressure is currently set too high, and the only method that I have found for reducing the pressure is to drain a radiator. This works, however the pressure then slowly rises again over a few days. I could experiment with the two controls on the pressure reducing valve, but would really first like to know how they operate.

If the isolating valve is opened then the pressure rises more quickly.

I have also attached a photo of the plastic knob showing the C <---> A label.
Brass PRV - plastic knob.jpg
Brass PRV - plastic knob.jpg (71.72 KiB) Viewed 4328 times
CH - pipework 1.jpg
CH - pipework 1.jpg (93.34 KiB) Viewed 4328 times
User avatar
By nt2
This is called an Automatic Filling Valve. The plumbing suppliers called it a combi valve.

The black knob was jammed (movement limited to about +/- 5 degrees) and releasing the brass screw on the near side did not stop pressure from rising, so I took it to the plumbing suppliers to be replaced. The leaking shut off valve is also being replaced with two, on either side of a removable external loop, and the single check valve replaced with a double check valve. After charging, the loop will be removed to prevent any further pressure increase.

Strictly speaking the automatic filling valve is mostly obsolete at this stage, however it does make filling to a set pressure easy, contains a sieve, pressure meter, and does not cost that much.

The Automatic Filling Valve contains:
1. Pressure Reducing Valve (set by the brass screw)
2. Isolating valve (Turn black knob full CW, ~2-1/2 turns, to isolate)
3. Single check valve
4. Stainless steel sieve
5. Pressure meter on side port

It appears to be best mounted with the water flow horizontal and the brass pressure setting screw section upwards. Debris nows falls downwards around the sieve (this is the way Caleffi recommend one of theirs be installed).

The sieve should be removed and cleaned ~once/year via the brass nut adjacent to the black plastic knob. At this time the black knob can also be exercised full OFF/ON/OFF a few times, and the brass pressure setting screw adjusted a turn or two +/- around it's set point.

The external filling loop will also allow accumulated debris from the mains supply to be flushed out via a drain hose before use, and thereby prevent it reaching the input side of the automatic filling valve. Before it could fall down to the valve, and new contamination appears when the water mains is restored after a cut off for local construction.

I did not discover what C and A mean, however fully CW is off.

After flushing/cleaning/inhibitor I will install a Grant Vortex magnetic filter near the pump inlet to help keep the boiler water clean in the future.
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