Double Disk Gate Valves
Double Disk Gate Valves
(OP)
- Has anyone had problems hydro testing at 200-250 if so can you explain
engineering or reasons why this happens.
engineering or reasons why this happens.
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RE: Double Disk Gate Valves
As the valve case is typically tested at the factory to much higher, e.g. twice the rating (you should be able to find this like the above permanently marked on the case) with the valve cracked or open , this would generally give confidence however that the pipeline containing the valve can be tested higher, but in doing so it would probably be advisable to test "through" the valve in a some open position e.g. with a new test boundary being a different bulkhead like a plug or blind flange, inserted "blank" or other etc.
While there are other reasons conventional metal-seated valves might leak e.g. even rather minor trash trapped between the gate and seat or scoring/damage previously caused by same, some modern compression resilient-seated gate valves may be more dependable for testing against closed gates bottle-tight, and also commonly carry a higher pressure rating of e.g. 250 psi. If you need more information, you may want to check the Mechanical/Valve forum.
RE: Double Disk Gate Valves
We are testing against a new closed double disk valve
as per municipal requirements 250#
There is only 70#'s in the street
once we get to the pressure up it bleeds back through the valve
RE: Double Disk Gate Valves
Air may be trapped in the line. The corrective action is to flush the line to remove the trapped air. Add an Air release valve if necessary.
RE: Double Disk Gate Valves
Can you just add a blind flange to the end of the valve and test against that? Testing against valves at close to their rated pressure causes difficulty as you have found out, which is why it is not recommended.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Double Disk Gate Valves
These are Mech Joint DD Valves. Many times we have to make the
connection to the main service then install the balance of our service.
Most plumbing insp. - once they see adequate pressure it's fine
every so often we get an insp. that wants 250# thats when we run into trouble
What I am trying to find out or if there is documentation that if you exceed
the rating - this is what happens ie: the first gate lifts which causes the second etc. etc.
Why do the valves fail? What is the sequence
RE: Double Disk Gate Valves
If you are not aware, leakage of 1 oz/hr/in of nominal pipe size has been/is actually allowed in even factory hydrostatic testing between the seats of this type of valve/per said specific standard (check specific manufacturer for any different/their expectations?) Depending on system configuration, filling, air evacuation and test requirements etc., it is possible loss of any water past the valve seats could cause the pressure to drop, at least some. Some variable designs of past and present double-disk valves may furthermore be better, or less subject to, regarding field leakage or field damage to seats etc. (that results in same in field tests) than others due to variable design features.
As has been mentioned in other posts, if you don't want any leakage by seats, other types of valves (e.g. resilient-seated gate valves) may be a better choice.
RE: Double Disk Gate Valves
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Double Disk Gate Valves