Bristan 1901 shower dripping

[richardindorset]

Had a dripping Bristan 1901 shower mixer that stripped its threads on the on/off flow control, so bought a complete new valve. Fitted it but I'm getting a slow drip when off. Cranking more on the on/off flow control makes no difference.

Just for a test, I took out the thermostat module and spring. The on/off flow control works perfectly, no need to use any pressure on the handle. No drips.

Could the new valve be faulty?

Obviously the spring in the thermostat module is pushing against the whole valve unit, basically forcing it open. As you close the valve it has to compress that spring. Just wondering if the pring pressure is making the valve body go slightly out of square o the o-ring doesn't seal.

Any ideas?

 

[CountryFan]

Could be the valve seating?

 

[richardindorset]

Could be the valve seating?

Initially I thought this too, but I've removed all traces of limescale and debris from the housing. The valve closes perfectly if the thermostat sping is removed.

 

[CountryFan]

Not entirely sure then. Maybe speak to Bristan?

 

[richardindorset]

Not entirely sure then. Maybe speak to Bristan?

Yeah, sent them an email. It's odd and annoying!
There are two springs in the thermostat module, I'm wondering if there is some sort of spring pressure balance that is slightly out with the old housing and new valve.

 

[richardindorset]

I think I have solved the issue.


As the main housing ages it gets pitted and scaled up on the flow valve sealing face. I have machined this off to get a clean sealing face for the flow control valve to close against.

Despite doing this, I was still getting a small drip when turned off.

As mentioned above, while trying different valve settings, I tried leaving the entire thermostatic control module out. This is a wax piston, a plastic carrier and a plastic shuttle, with two springs. With this assembly removed, the flow control valve seals properly. No drips.

I assumed the thermostat return spring may be keeping the flow valve open, so I tried just removing that spring but keeping the rest of the thermostatic control valve in. This started the leaking again.

After taking a few measurements, I discovered that the thermostatic control valve shuttle (clear plastic part) actually also functions as a limit stop on the flow control valve. This explains why removing the thermostat module stopped the leak.

As the clearance for the flow control valve is now opened slightly do to having machined off the sealing face, the valve was not sealing and could not close any more due to the plastic shuttle stopping it.

I tested this by taking 1mm off of a spare plastic shuttle. This worked and the shower no longer leaks. Unfortunately a side effect of doing this is that there’s no longer enough hot water due to the shorter shuttle, so I will have to machine a small amount of off the end of the flow valve piston.

This discovery is interesting because as these mixer valves age and become pitted, you often find you have to crank a bit harder on the flow handle to shut off the shower completely. Eventually you are just crushing the plastic temperature control shuttle and of course putting a lot of strain on the flow valve threads. These theads are very fine brass and eventually strip. This is why I bought a complete new shower valve in the first place.

Now that the flow valve seat is clean, new brass and the piston is able to close against it completely, the shower shuts off properly and there's no need to use any force at all on the handle. Hopefully the theads on this valve will last.

Quite a journey, but worth it in the end!