how to fix a persistently leaking water valve seat

[holt]

As per the attached photo and web page, what he calls a 'compression valve' but which I call a 'valve seat', made of brass, keeps eroding across the 'face' of the valve, where the rubber gasket presses against to shut it off.

The same thing happened to me. You put in a brand new valve seat, and within half a year or a year, it erodes across the 'face' and a runnel or groove is formed, resulting in an unfixable leak. It does not matter if you use a 100% brass valve seat, or a nickel-plated one. They both erode.

How to fix. The 'fix' is simple to describe, but a little tricky to perform, but my 'fix' has been going strong for five or six years now with no sign of quitting.

Take a new valve seat, and rough up the 'facing' (where the rubber presses against the flat circle of the valve seat), using about 200 grit sandpaper. Don't try to reform it; just rough up the 'face'.
Next, take electrician's solder, and create a ring-shaped layer of solder on the surface of the valve 'face'.

This is the 'easy to describe, but tricky to do' part. I had to use a big old-fashioned electric soldering iron, mounted in a big bench vise, pointed straight up, to put the brass valve seat on and heat it up. Before you do that, you need to apply a thin layer of soldering acid paste to prevent a micro-thin layer of corrosion from forming when heated up, which would prevent the solder from bonding. At the same time, you want to avoid getting solder on the valve seat threads, which could interfere with screwing it back into place in the valve body. If you get it in the threads, just heat the entire valve seat up and drop it on the bench a few times to shock it physically and knock the excess molten solder off.

The really tricky part, is that, as you apply the solder to the valve 'face', there will be a persistent tendency for the solder to form a 'bump' on one part of the ring of the valve face, and a dip or dimple either next to it, or opposite it, on the ring of the face. I had this happen repeatedly. It was so persistent that it was positively mystifying. I tried getting an extra-thick buildup of solder and sanding it all down flat, and I kept wearing through the thin layer of solder and exposing tiny areas of brass on the valve face. Time and time again, over and over, and over and over, I ran into this problem. Finally, after about an hour, I succeeded in getting a uniform layer of solder on the ring of the valve face that was smooth and flat. Then, I had to do it to the other valve; because there are two valves; 'hot' and 'cold'.

I did this about five or six years ago, and I have not had to service the valves ever since. Just that tiny layer of solder, bonded to the brass valve seat. That's all I did. This has been the result. 

edit: If you must, you can try to salvage and reface an old valve seat with a groove in it. Just rough it up, including the groove, and refill the groove at the same time as you reface the valve face. Come to think of it, that's what I did, but mine wasn't as bad as the one in the photo. I fixed the leak and it stayed fixed.

[Ath]

Where is that valve used?
How often per day/hour/minute (or whatever scale seems appropriate) is the valve opened/shut?

[holt]

The bathtub. About two to four times per day.

[IainB]

@holt: Thanks, that's very interesting.
The corrosive erosion that seems to occur in plumbing has always mystified me, because it is presumably attributable to some sort of electro-chemical action in the water supply, but it doesn't seem to matter which water supply, or even whether the eroded part is made of a good or inferior alloy.

So I deduced that the unknown could well be the chemical composition of the rubber/neoprene valve seats.
Your fix is interesting. The metal in electric solder is usually inert and is a fusible alloy made up of 2 or more metals (typically including tin and lead). Using it as you have done would generally leave an inert metal layer on the face of the valve seat that was treated, and the proof is in the pudding - i.e., it works and it lasts.

However, using such alloys in the plumbing might not be a particularly good idea from a health standpoint, as minute traces of the inert  substance (lead, tin etc.) could leach into the potable water supply from that faucet, contaminating the water with metals that are accumulative and toxic in humans and which - even at very low levels - can cause serious and irreparable long term and sometimes devastating damage to various organs (including brain, liver, kidneys) - especially children and the unborn. For this reason, in most Western countries there are very tight standards that have to be maintained by plumbing component manufacturers. For example, only certain maximum amounts of lead or molybdenum are allowed in tap and valve casting alloys, and some manufacturers pride themselves in achieving significantly lower levels in their castings than those maxima that are permitted by the standards.

Similarly, it's not a good idea to store/drink water from the heated hot water cylinder/supply, because it may contain traces of the heavy metals that the hot water cylinder has been lined with to prevent corrosion at high temperatures.

One can safely assume that what you have done in your innovative approach will have probably compromised your potable water supply to an unknown dangerous extent, and it will remain such for as long as the treated valve is left in situ - so it will be passed on unbeknownst to and unsuspected by any future buyers/tenants of your house, and their children (if any).

So the moral here is undo the fix and don't mess with the composition of components in the potable supply - and the reasons are varied and well-documented (e.g., do a DuckGo search for "contamination of potable water supply", and "toxic metals used in plumbing hardware", "toxins in potable water", etc.). In the literature, you will be able to find descriptions of how quite large numbers of people have been poisoned/harmed and/or killed by similar well-meaning and accidental events affecting the potable supply. Over the years since probably the 1920s this has given rise to a whole raft of incrementally improving and increasingly more stringent international and local governments standards to eliminate dangers to people from the risk of toxicity in the potable water supply.

Sorry to "rain on your parade", but, as someone responsible for advising on the management of some old and some new apartment blocks, I am acutely aware of these issues as I have had to figure out how to get old/defective or non-standard water system installations fixed/upgraded so as to comply with national and local government health and safety bylaws and standards. If one or more units in an apartment building are reported to have "leaky homes syndrome" (poor/defective construction) or potable water supply contamination issues, then the resale value and potential rental values of all of the units in that block could fall (say) 50% or more overnight and stay there until the building has been fixed and officially certified as complying with prevailing standards. If the financial aspects weren't sufficient motivation to fix things, there is the additional  motivation of heavy fines for not fixing it within a reasonable period of time.

[holt]

It is lead-free solder.