keep breaking gate valve stems

[rzjim]

I work for a water supplier and the operations crews have been assigned the task of operating all the valves in our distribution system. The crews are newly formed and do not have alot of experience. Just recently we have found 4 broken 24-inch gate valves. I suspect the crews are using a hydraulic operator and are setting the force of the operator too high. My question is: On a 24-inch gate valve, probably a Chapman installed in the early 1900s, what is the force that the hydraulic operator should be putting on the stem? I think the stems are bronze alloy??? about 2-inch diameter. Any thoughts? BTW this is my first post and I think this looks like a great forum!!!
Thanks in advance
Jim

 

[svanels]

I suspect the crews are using a hydraulic operator

???

How do they break? in open or close position?

I have seen a lot of "inventive tools" used on valves, ranging from the "calibrated" sledgehamer to a pipe handled by 4 guys

 

[rzjim]

The water utility I work for has purchased a couple of Wachs valve operating machines. A 24-inch transmission main is being cleaned and cement mortor lined. There were two 24-inch gate valves with broken 4-inch bypass valves. I had an operations crew go out and check all the valves on near the two broken valves. Typically all valves are supposed to be open. The crews went out and tried to close & open all the valves with the valve machine. In 2001 someone else had operated the valves and closed the valves with about 2500 pounds of force set on the machine. This year three more valves were broken with about 1300 pounds of force. We are petty sure the stems are breaking. I can not (do not know where to) find any information on how much force should be applid to the valves when operating them. I have not confirmed this, but I believe the stems are 2-inch diameter with acme threads made out forged bronze alloy.

 

[svanels]

Hm.. could it be that the operator is trying to open an already open valve? Are the 4" valves breaking or the 24" valves breaking?

Are they using the hydraulic tool on both types of valves, if so what are the limits?

Can it be that they use the 24" setting to open a 4" valve?

We are petty sure the stems are breaking

Did you see a broken stem? Your answer indicates that the information is reported.

Probably a visit to the "battlefield" could reveal some more clues.

 

[unclesyd]

You need to get the valve steams to Metallurgical Lab for analysis of the failure.

You might have a electrochemical reaction going on within the stem that makes it considerably weaker. This is especially true for a valve that old.

Just for curiosity how pure is your water, both now and historically?

 

[rzjim]

Thanks for replys.

I'll respond to reply in order:

1. Hm.. could it be that the operator is trying to open an already open valve? Are the 4" valves breaking or the 24" valves breaking?

Typically all main line valves are open and bypasses are closed. When the valves were installed a written record included the direction to turn the stem to open the valve and the number of turns. One valve had a broken bypass the rest (four) are beoken main line.

2. Are they using the hydraulic tool on both types of valves, if so what are the limits?

Can it be that they use the 24" setting to open a 4" valve?

I'm not sure. They are not supposed to, but may not know. The limits are why I started this post. I've researched the manufacturers catalogs, but they do not provide that information. I'm looking for the purchse orders in some old records, but do not think I will find them.

3. Did you see a broken stem? Your answer indicates that the information is reported.

Probably a visit to the "battlefield" thumbsup could reveal some more clues.

We will be excavating the valves in a few weeks. I will be able to see whats going on then.

4. You need to get the valve steams to Metallurgical Lab for analysis of the failure.

This is a good idea. Do you know how much it will cost? I will ask to see if its something I can get some $$$ to have done.

5. You might have a electrochemical reaction going on within the stem that makes it considerably weaker. This is especially true for a valve that old.

Just for curiosity how pure is your water, both now and historically?

The water is drinking water. It is the same source since 1930. The only treatment I'm aware of is sand filtration and a minimal amount of chlorine for disenfection. That's about it!!

Thanks again
Jim

 

[JimCasey]

You're going to have to replace the stems, and I suggest you use 17-4 PH stainless heat-treated to around H800. The thrust nuts should be bronze. The bronze nuts with the stainless thread will be non-galling and should last you past retirement. Furmanite recently bought Flowserve's repair division, and those guys should be able to help you, reverse-engineering and manufacturing replacement parts, with minimal disrupton of the water supply. These guys sweep in and work outages in power plants, with truck-mounted machine shops. THey should be able to handle this pretty well.

Furthermore: Interview the operators who experienced the failures. Look for telltale signs such as 24-inch-plus biceps, thumbs that do not quite oppose, large numbers of banana peels and pinup posters of Jane Woodall in the break room.

 

[unclesyd]

rzjim,
The reason for the water purity question is that the purer the water is they more the possibility of "demetalization" of a brass or bronze. This is the dissolution of the material and selectively redepositing the copper. The component where this happens will normally look good but will have no strength. This process is easily discernible.

As far as prices I have no idea at the prices charged for a quick failure analysis of a part such as yours. I would start making a few calls to a local lab if you have one. There are also some online companies that provide this service. I would hope your utility company would have a materials engineer available. Whoever you use just ask for a lab report and not a formal report.