Gate Valve failure modes 5

[gargravarr]

My team has been tasked to look into a maintenance program for a computer center water cooling pump system (water -> valve1 -> centrifugal pump -> valve2 -> cooling system).

The system has two rising stem type gate valves and I need to be able to detail common failure modes and how these will be monitored. I don't have any more information than that sadly (good ol' management), and I'm a bit of a novice in relation to valves.

I'm certainly not asking for the full solution, you guys probably have a lot of work to do, but any terms/concepts to research further would be highly appreciated.

 

[JimCasey]

(1) Gate valves leak through the seats. Determine what the limit of acceptability will be for your seat leakage in your application.

(2) Packing in gate valves wears rapidly if the valve is actuated much...you're dragging the full line diameter of the stem through the packing and putting a lot of miles on it. Again-how much leakage can you tolerate before the situation needs to be remediated.

(3) protect them from freezing. Freezing will burst the bonnet and the valve will be destroyed and everything nearby will be flooded.

 

[Ashereng]

When you say "common failure modes", do you mean typical ways a gate valve will "malfunction"?

Are you considering the actuator and accessories as part of the valve, or separately?

A gate valve that has been closed for a while may also "stick" when you try to open it. Maybe due to some corrosion.



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Albert Einstein
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[vpl]

Depending on the quality of fluid (such as untreated river water) and the valve material (such as carbon steel), it is certainly possible for gate valves to rust. This can either cause the valve to "stick" as Ashereng mentioned or for the disc to pull away from the [oooh, terrible bad senior moment!!: what is the piece called that connects the valve disc with the acuator? Oh yes...*] stem so that you think the valve is full open and it's not.

[*I've been staring at valve drawings on and off all day...you'd think the word would just come to me!]

Patricia Lougheed

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

 

[jte]

Another potential failure we see on occasion is a dropped gate. This is when the valve stem breaks inside the valve and the gate drops, closing the valve but the stem is still up leading one to think that it is open. One way to avoid this is to put the stem in a horizontal or lower plane. In some places block valves for safety relief devices must be installed with the stem horizontal or lower.

jt

 

[gargravarr]

Thanks guys, I've got something to go on now and can continue from here.

For the curious; the water is clean and is cycled around the system. The valves are steel, and are left open until they are needed to close for maintenance.

cheers,
G

 

[MikeHalloran]

You need to read up on water. Very few fluids are more corrosive.

Gate valves leak internally, leak externally, stick open, stick shut, and get fouled by crud that's not supposed to be there, including pieces of the valve itself. Their only virtue is that they're 'cheap'.



Mike Halloran
Pembroke Pines, FL, USA