Do refurbished valves take a set?

[Peter69_56]

I have had a slightly different issue. Have an OMS older style manifold. With both valves closed randomly one valve will burst forth losing significant air. Close it more and then its ok? Never seen a valve seal temporarily for a period of say 2 hours then let rip with a roar which can be shut off? Yes the manifold needs servicing and I will get it done at the next hydro in a few months time, but was curious as to the cause

 

[Diver0001]

sounds like a worn seating that's allowing a thread to slip.

Either way that's not normal. I'd say get the part replaced (probably make chrpai make some smart-ass comment again... LOL)

R..

 

[Colliam7]

The valves were refurbished but a couple of tanks really need cranking on the handwheel to tighten- even then there is a subtle leak which means I'm puttig a reg on the tank overnight to prevent surprises the next morning. . . . Do tank valves take a set like a reg hard/soft seat? Or should I get back to the shop and say wtf?

The answer (should you get back to the shop) depends on what tools / parts you have available for a field repair, and how convenient it is to take the cylinders back to where you got them. If convenient to return them (and you paid for functional cylinders and valves), then do so. If not, and you have some wrenches - AND a valve parts kit or two, then the fix may be easy, as several have noted.

I agree with halocline that the first step is to put the cylinder in water (valve closed, cylinder pressurized) and visually observe the source of the leak. Remove the handwheel before doing do. As simple as it may sound, you want to be sure the leak is coming from the valve, not from the neck of the cylinder. I had a customer bring in a cylinder for ‘valve service’ because of a slow leak. When I put the cylinder in water, the bubbles were coming from the neck of the cylinder, NOT from the upper portion of the valve. Turns out, there was quite of bit of corrosion around the orifice on the cylinder. I needed to (vigorously) clean the valve gland at the top of the cylinder and replace the neck O-ring, to stop the leak.

In your case, however, it appears that the source is the valve, since you indicate that putting a reg on the cylinder overnight stops the pressure loss. That situation also suggest the leak is coming through the valve itself. Examining the valve 're-assembly' is the next step. There are several 'adjustments' that you can make, but your description suggests the probable fix will be a part replacement, not an adjustment.

In servicing valves, the biggest culprits, as far as leaks, that I see (your experience may vary) have been:

1. Worn / damaged nylon seat on the HP plug. These seats do take a bit of a ‘set’. Yes, the seat is hard nylon, but it is being forced against a metal shoulder surrounding an orifice, as the handwheel is turned to close the valve. Given your description that the valves 'really need cranking' to tighten and close, I suspect the plug seats are worn / gouged / cored. If the HP plugs were re-used when the valves were 'refurbished', that is a possible source. Further damage to the nylon seats may have been done as the more 'cranking' was used to close the valves. It is also an easy fix (and relatively inexpensive), IF you have a new one to install. My bet is on this one, IF the pressure loss is completely stopped when you put a reg on the valve. But, you actually may have several leak sources, so if you do the field repair, check them all.
2. Mangled crush washer. These are intended to be a one-time use item, but I have seen more than a few people re-use them, even after seriously deforming the washer to remove them during dis-assembly. This is also an easy, inexpensive fix, IF you have a new one to install.
3. Burst disk insufficiently tightened. Given your description of putting a reg on the valve, this is also an unlikely source. But, if the valve was 're-furbished', presumably a new BD was installed. There are torque specifications for tightening the BD. I have had a few leak after tightening to those specs. MY specs are now ‘1) tighten to stipulated specifications and test; if leak observed, 2) continue to tighten until the BD does not leak’.
4. Bonnet nut simply not tightened sufficiently, or bonnet nut damaged (cracked) / corroded. This (not sufficiently tightened) is not all that uncommon, depending on the thoroughness of the service tech. This is also a potentially easy fix. Close the valve to the extent possible. remove the handwheel, put a wrench around the nut and tighten. If the bonnet nut is damaged, that's a part replacement, not just a simple 'adjustment'.
5. Nylon packing ring damaged or omitted entirely
6. Valve stem O-ring damaged or omitted entirely

The last two are not very probable, but I mention them for the sake of completeness.

Good luck.

 

[captain]

I have found more than one used valve with the wrong or mis-assembled parts.

 

[halocline]

I have had a slightly different issue. Have an OMS older style manifold. With both valves closed randomly one valve will burst forth losing significant air. Close it more and then its ok? Never seen a valve seal temporarily for a period of say 2 hours then let rip with a roar which can be shut off? Yes the manifold needs servicing and I will get it done at the next hydro in a few months time, but was curious as to the cause

Wild guess would be similar to what Diver0001 said. The seats are typically hard plastic plugs imbedded in threaded rods with a slot on the other end. I guess it's theoretically possible for the threads on the seat to be worn enough so that with the force that air is pushing on the seat it jumps a thread. If that's the case and the threads on the seat itself are okay, maybe the threaded part on the manifold itself is worn, in which case I guess it's off to the trash heap. Or maybe it's just the wrong size threads on the seat.

 

[Peter69_56]

Ok thanks guys, on that basis and from what I found, I suspect it might be played with and thus rubbish dump quality. On purchase I found the cylinders empty (when they stated they were full), and after test and on filling found a bursting disc leaking. Emptied it and found some clown had put in 2 bursting disc plates on one bursting disc. At the time after discussion with the dive shop we thought they might have burst one and did a temporary repair with 2 incorrect discs. Given your latest thoughts, I suspect the previous owner was a back yard scuba mechanic (as well as an instructor, so it just goes to show that being an instructor doesn't make people ethical or honest) and did his own repairs not to standard. Looks like I need a new manifold, and given they are $100 to service, it would be simpler to spend $175 and buy a new one and junk the old one ensuring no waste in attempting to repair it. It also gives me the latest style manifold rather than the older style OMS type.

 

[Diver0001]

Wild guess would be similar to what Diver0001 said. The seats are typically hard plastic plugs imbedded in threaded rods with a slot on the other end. I guess it's theoretically possible for the threads on the seat to be worn enough so that with the force that air is pushing on the seat it jumps a thread.

Or that someone serviced it and replaced the seat with the wrong sized part.

R..

 

[halocline]

Or that someone serviced it and replaced the seat with the wrong sized part.

R..

As I said

Or maybe it's just the wrong size threads on the seat.

 

[Fishpie]

It's not unheard of for burst discs to be doubled or even plugged on purpose.
European valves don't even have them.

 

[Peter69_56]

With this set of twins, one disc had double discs, and the other was set with a single (as per normal). Also given the issues I have had with the valves, I suspect this diver was a person happy with jerry rigging gear to get it to work, rather than a predetermined plan. My assessment would be "Stupidity" at work. I like things done properly so they are reliable, not a patch job over patch job over patch job etc.