About pneumatic control valves 2

[TEOMECH]

Can anybody give me any advanced cause about the continuous damage of diaphragms(reinforced) of pneumatic control valve used for boiler feed water? (reverse acting,air quality good)

 

[Ashereng]

Teomech, you may want to delete your post from this forum and re-post in "valve engineering" forum.

You may have more luck with responses.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[JLSeagull]

In my experiance the typical control valve actuator diaphragms are very robust. Perhaps you have a high pressure, pre-heated boiler feedwater valve that is too near the actuator diaphragm. Some old boiler feedwater regulators such as Copes Vulcan may be an example as compared to a typical control valve.

What are the conditions and specifics that apply to your situation?

Also, Ashereng is right that the valve or measurement forum may include more responses. Consider posting with the details at valve engineering.

 

[rmw]

Diaphram actuated control valves have been used for BFW service since Noah used them on the Ark. Well maybe not that long, but for a long long time and have a good service record. The old regulators did a good job in their day too.

rmw

 

[ya1939]

It appears to me a manufacturing defect.Try and use a different make.

Regards
Yousuf Ali

 

[TEOMECH]

Thank you all for your valuable posts,but i ve been realized that maybe there is a problem with control air pressure.Overpressure even 0,5 bar it can damage the diaphragm.So i am searching to that direction. For you information the valve is under guarrantee period and there is a claim to maker.Also consider that this type supposed improved type by the maker and before its first broken diaphragm the maker ensured that it is unbreakable....But the maker it is not possible to be changed because of a contract....

 

[richs]

Hiya-

Now, I'm way out of my field here, a computer guy, but have
a little bit of knowledge in the area. I might suggest that
you incorporate a surge tank in the design to mitigate any
sudden pressure changes which I can envision would be
possible in a feed water system. Such surges in an air
controlled system could easily drive the instantanious
pressure in the system over spec.

Indeed, a small coupon in the circuit can help on the surge
tank can be used with various "delaying" properties easily
changed by choice of coupons on the input side of the tank.

Hope this helps. Again, sorry, I'm out of my area of
expertise, I'll go back and start suffling my "bits" about
again.......

Cheers,

Rich S.

 

[Scotsinst]

1. Check instrument air supply pressure versus max allowable pressure for the diaphragm.
2. Assuming your valve has a positioner, no boosters and the filter/regulator is set for the correct air supply pressure, the diaphragm should last many years.

 

[danw2]

Those little 1.5" diameter pressure gauges that get put on regulators or positioners are only 3% at best and any gauge is toast if it gets overpressured because the bourdon tube gets stretched or a link bends.

Why not check the supply line to the positioner with a 2nd gauge and see what it reads? Just becuase that cheap little gauge says 50 psi from the regulator it isn't necessarily so.

I'd be curious how the diaphragm failed on a fairly new actuator. Pin hole leak? torn or ruptured fabric? where?

The valve isn't sitting on top of the uninsulated boiler shell at 260°F ambient or some such overlooked possibility?

Dan

 

[jgv]

Maybe your problem is the temperature at the top of the valve, and you need another material for the diaphragm that supports the temperature, you can check in a fisher governor catalog to find the material of the diaphragm you need