Valve stiff under Pressure?

[Segs14]

For some reason when my tanks are under pressure 3000psi the valves and the manifold valve become stiff to turn but when the pressure drops below 1000 psi they start to turn as they should. What would cause this? Could their be something wrong with the high pressure seats.

 

[Plumb bob]

As the pressure increases there will be an increase of friction in the threads of the seat and I would think this is most likely the main cause of the increased stiffness.

 

[widget]

You will have a slight increase in turn friction as the pressure increases, but it should not be so major that its difficult to turn the valve open.

If it remains difficult to turn,there could be internal corrosion or dirt in the threads, strip them down (empty the tank first obviously) and clean the valve and internals in a mild vinegar / water solution, then reassemble coating the threads with a small dab of silicone grease and using a new kit if necessary. The water will just wash the grease away after a dive or two, but it assists in making assembly quick and easy.

This is a simple operation well within the scope of most with a few spanners and a screwdriver and shouldnt take you more than 30 minutes, valve removal, decorrosion and replacement included.!!

Spin away and feel the differance.

 

[Segs14]

Yea its more than a slight increase. What i also noticed is that with the valve closed if you take the knob of and try to unscrew the cap without turning the valve post it is under pressure which is should not be.

 

[JamieS]

I have seen this problem many times in rental tanks. Then, it was usually the teflon washer that sits between the valve stem and the packing nut that holds the stem in place. The washer rubbed between the stem and packing nut long enough to dissapear or at least thin to uselessness. If this is the case though, sometimes there is so much friction between the packing nut and the valve stem that losening the packing nut causes the stem to turn thereby opening the valve while taking it apart. (read: potential for flying metal parts if under pressure)

So, check that our as well as cleaning it up like Widget describes.

Good Luck

 

[Segs14]

the weird thing is that it was a brand new kit that was put in. i have a new kit and am going to reclean everything and put it back together. I am just curious to know if something was up with the high pressure seats because it was doing it on all three valves. they were fine when first filled but after they sat overnight it was a pain to turn

 

[captain]

If all three were rebuilt and now all three are hard to turn = bad rebuild, possibly wrong kit or sometimes kits are generic and all the parts in the kit don't necessarily all belong in all valves the kit is for.

 

[Segs14]

its a halcyon valve with a halcyon kit. I dont think dirt is an issue because they were spotless.

 

[knotical]

Many valves have torque specs, as seen in this document (albeit not a Halcyon document):
http://www.scubaengineer.com/documents/thermo_maintenance_manuall.pdf
Is it possible something was over tightened?

 

[widget]

If all three were rebuilt and now all three are hard to turn = bad rebuild, possibly wrong kit or sometimes kits are generic and all the parts in the kit don't necessarily all belong in all valves the kit is for.

Yah, I agree, if they are clean, then it sounds like a bad rebuild. Maybe some of the washers were omitted, or it sounds like either the stem or the seat is wrong and binding somehow, best to strip them down yourself (I say again, make sure theres no air in the cylinder ) and check, install a correct new kit yourself, and reassemble properly.

As a matter of interest where are the valve made? If you have a pic of them or they have a "Made in ???????" stamp somewhere, I may have specs available if I can identify the manufacturer, although its such a simple procedure they arent really necessary.