Outside valves, OT

ahackwor

Member
Join Date
Jul 2006
Location
Michigan
Posts
40
Well it's -4F today and I have some frozen valves, imagine that. Our typical valve is a steel ball valve with an air actuator, solenoid, and limit switches. Sizes range from 1/2" to 6" with 2" being very common. These are full open / full closed valves, not control valves.

The problem is not the fluid in the pipe or the valve itself. We use electric heat tracing as needed on the pipe lines and valves. The problem is in the air actuator or solenoid. Any tips or tricks to keeping these from freezing? The utilities guys claim the compressed air is dry.

Is anyone using an electrically driven valve for applications like this? Can you recommend a brand and model?
 
I would bet it's some fluid in the line, I have seen plants use compressed nitrogen for outdoor valves for this reason.
 
nobody can make the air dry enough to get to 0 F , not with a cooling drier, nor with a dessicant drier.
it is ice or cold oil in the valve, put some alcohol or antifreeze, benzine depending on safety in the airline and just give it some commands to open/close to get the stuff inside the cylinder.
my old diesel will not start as the gasoline will not explode due to the low temps.
(here we have one of the hottest winters ever.)
 
Shooter I disagree with almost everything you just said.

If you have an appropriately sized drier then this should not be happening. You have condensing moisture in the lines. You will probably require a drier that has a dew point sensor on it and can pull down to at least -20.

"Dry" is a relative term. The op needs to know what the dew point of the air exiting the dryer is to determine if the air is "dry" enough.

I would be surprised if adding alcohol or benzine would help as the vapors would condense inside the air lines and while they would freeze they probably would negatively impact the function of your valves.
 
It doesn't have to be air issue, there are also mechanical parts involved like seals, o-rings, if they are not specified to withsdand sub zero temperatures they can cause problems.
 
I tend to agree with Shooter, at least about the cause of the problem. Frosting in the air lines is one of the reasons I always try to go to electrically operated valves. When they are mounted outside I always include an anti-condensation heater ant T'stat in them.

It is possible to get air dry enough to avoid frosting in severe cold climates (Houston doesn't count!). In practice, though, it is very common to have frost in the pneumatic lines for outside mounted valves.

I've had decent luck with Rotork, AUMA, and RCS. RCS is less expensive but also not as reliable. I've used Limitorque (expensive and lousy service) and EIM (expensive and bid as a barn) too.
 
Last edited:
Houston an be a tough place because of the humidity. When plumbing air into -20 through 30 degree refrigerated process areas it can cause a lot of problems. For those temperatures electrically actuated valves are probably better. Heat tracing and thermostats would help also.
 
Most actuators have a generic statement in the spec sheet and I&M manual to the effect that the air has to be dry:

34fbak5.jpg


Frozen water in the solenoid is so common it shows up in troubleshooting guides:

velkci.jpg


Air can be dried to -40 deg F dewpoint. When it is it's called instrument air. The ISA S7 spec addresses air quality for instrument air. Since the demise of pneumatic controllers and pneumatic transmitters, emphasis on clean dry air has diminished, until a cold snap when freezes the pneumatic controls.

The gist of the spec is a measured dew point:
-----------------------
Instrument Air Quality Standard (ANSI/ISAS7.0.01-1996)

Instrument air quality standard establishes four elements of instrument air quality for use in pneumatic instruments

1. Pressure Dew point
The pressure dew point as measured at the dew point outlet shall be atleast 10 deg C (18 deg F) below the minimum temperature to which any apart of the instrument air system is exposed.
-------------------

Many places just put a coalescing filter on the compressed air and call it the product 'dry'.

People whose lives can depend on dry air, like the north sea oil rigs, have specs for the output of instrument dewpoint analyzer to tie into an alarm system, like this Norshok spec:

2dvtyer.jpg


The seals in ball valve pneumatic acutators can be a different material for lower temperature operation, although that's more for leakage/sealing performance than for protection against ice:

ebdjdz.jpg
 
-4F I wish, it's -46C with the wind chill here today. There are a few things not woking outside today including me. :)
 

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