Safety Valve seat problem

It seems odd to me to use metal on metal for water. Would a neoprene seal solve all the problems? Or ar there impurities in the water which would damage a soft seal?

I think reciprocating pumps do have metal on metal type of pressure release valves . I have seen some triplex pumps that have metal -metal contact with an additional rubber interface . Howvever this type of pump is purely metal to metal .

As for impurities , yes, the pump is used in carwashing where the water is usually reused . Suction filter can filter only upto 600 microns.

Thanks for the reply .

I agree but he seems to want to use metal on metal.

You said because of machining problems of needle and seat that they will not seal. this problem needs to be resolved. To correct the immediate problem take and re-seat valve. This can be done if the metal seat is soft enough with a hammer and a slight blow of the needle in the seat. If that don't work try lapping compound. Turn the needle in the seat with lapping compound until evidence of good contact around the seat and needle.

So you have a pressure actuated mechanical valve with high pressure bypass. How did you determine it ws the valve? I mean are you 100% certain this is the culprit. Is there any contamination. How big is system, what kind of psi are we talking. Ambient temps. How old is valve. where is said valve manufactured. Is it a reputable company? What do mfg.'s specs claim.

All else is speculation. The LAST thing I would be doing is analyzing valve tolerances. Unless this is a specialty valve mfg'd specific for your unique application.

What is this system anyway?

Sounds like you have a scrached or damaged seat. Also look for surges in your pressure system that could be opening the valve. Different size in supply lines can cause surges in pressure.

For the measurements for the seat I would just go buy a high pressure valve take it a part and measure or call a manufacturer.

sorry. I mis read the question first go round. Is this an off the shelf valve you are using or is it specialty made. Typically one would want the wear component (in this case the plunger?) to be less hard or to wear faster than the more costly or permanent component (in this case seat? valve body?) There are thousand of valve configs - each with their own unique quirks. I spent many years testing aqueous chemical, gaseous chemical and water delivery systems for the semi-con industry and these types of issues arose often. Again I say chasing the valve specs can be snipe-ish, so unless repair or warranty or your own prod is in question I would make certain I needed to answer this question. As a machinist I know that a truly accurate analysis of these features is often not readily attainable w/out some real challenges.

no this is not an off shelf valve , it is specially made . The spring load can be increased by tightening a nut thus increasing the valve opening pressure but I presume this is not proper as the pump rated pressure shoots up to 24 bar , whereas the rated pressure is only 18 bar .

The plunger is heat treated , so the wear element in this case is the seat .

do you have flow restriction downstream of the valve? ie; too small orifice/outlet diameter. 24 bar on outlet side of pump? more data please.

There is no flow restriction . The discharge from the pump is through two outlets , gun hoses which are used for car washing . The pressure gauge is fitted at nearly the same location of the safety valve on the pump head . The pressure is set at pump assembly area during pump testing .

The testing procedure consists of running the pump and then adjusting a bolt which varies the spring load on the valve . the bolt tightness is adjusted such that the valve opens at 20 bar . The gun outlet is closed to increase system pressure and thus check whether the valve opens at the required pressure or not .

Dear sir,

When the subject valve and seat arises ,the prime criteria is valve seat matching.Next only material.so try lapping.Then go for silicon carbide coating or go for automotive engine valve materials.

sankar

Try this. Make the seat flat. The tapered end of the plunger should keep a constant seal in the hole even as the seat wears down.

I think your problem is in the manufacturing process more than the design. In this day and age the tolerances for a seat valve like this should be easy to achieve. If they can't I'd reject the lot and find a manufacturer who can meet the drawings.

That said I have some questions: Why are you using stainless steel and not bronze? Chemical reaction? Are the pressures that high? Are you sure that the spring force is proper? Maybe the manufacturer has that wrong too?

Good luck

I've got to agree with the multi colored cat. As I stated before, speaking as a machinist AND as aqueous chemical/process piping testing technicician AND as 3rd party quality assurance rep to the laregest chip manufactures in the world (which, admittedly, does not mean that I know squat), find a manufacturer who can meet your needs and replace the valve. Design spec should be clearly identified to meet your needs. The LAST thing (if at all) that I would do is begin my own QC evaluation of a valve that has been in service. If the scope and nature of fault are of the "must know" sort, you are really up against a Rubiks, and potentially sniping yourself. If there is a liability concern or warranty issue I would go to a third party. But thats just me, and Ive got a thing for production.

Anything can be done, with a price tag.

Both sealing surface need to be grinded and need to be concentric. Unless your design will compensate for that. You'll either need to remachine the seal and plunger or replace plunger with softer material.

Pineapple

304 stainless seat is not desirable. The water will cavitate strongly as it flows out the valve seat causing rapid erosion (and seat failure). This needs to be a hardened cabide seat. Stainless on stainless is NEVER recomended due to substantial risk of galling and rapid failure.

You may also have to install a small pulsation dampener just ahead of the pressure relief valve to preent rapid chattering.

Are you manufacturing/designing the valve in question 'in house'?

Actually this is a very old model of a Uraca pump . We are giving the drawings to an outside supplier who uses a centre lathe to cut the chamfer on the seat . Perhaps that's why all these dimension issues come out .

we are working with another supplier to try and manufacture the parts in CNC lathes where better repeatabilty can be obtained .

Ahhh. Okay. First -I am going to assume the manufacturer you are using is a relatively small 'job' shop so here is the deal from a machinist/QA manager's perspective:

If you are reverse engineering the valve to seat configuration in order to trig out the angles based on large diameter to small diameter, the use of hand held measuring tools may not suffice. Use a latex or dental mold material to create a profile for measuring seat dimensions with use of a comparator and also measure plunger. If a CMM is available this would be an option too. All subsequent production analysis could potentially be based off hand tool measurements once the baseline criteria is met ie; a functioning valve, depending on the functional accuracy needed.(The cost to 3rd party should be about the same for CMM or comparator analysis and the accuracy you are needing will be met.) There is alot of discussion I can follow up with her if this is the direction you feel you need to go. The point here is that tools such as calipers/blade mics etc. may not get you what you want. I am thinking perhaps you have a valve body and are replacing a plunger - well whatever - if this is a metal to metal config one or both components IS worn. Normal thinking tells me it should be the plunger but regardless this can create problems for part construction, accuracy etc.

If this rhetoric is all, well, rhetoric, then the advice about a damaged seat is the direction to go. when you isolate the psi gage - eliminating the valve- are you seeing the desired pressure? Are you sure there is no overpressure/pressure releif valve upstream (at source) causing you grief.

Nevermind that paragraph.

I just re-read some prior correspondence. SO IF YOU ARE CERTAIN the system is not functioning properly as a result of this item OR that this ITEM is not functioning properly SOLELY as a result of this feature - describe your inspection methods. Are the dimensions established from the old manufacturers original prints or reverse engineered? Why were these metals chosen. Are we 100% certain an off the shelf valve wont suffice? Carter, Nupro, Carten, all make industrial valves and valve components. Perhaps one of their reps could get you the valve config or the name of some one that distributes similar.

I am interested.....

I agree that the poroblem may be in the desgn more than anything else.

I would try going with 304 for both the plunger and the seat and try Kolsterising it to give you a surface hardness of 68 HRc.

www.kolsterising.info

Any idea of prices / costs?

The angles between your seat and disk are designed to have different angles. This makes the contact area very narrow and allows for repairs later on in the life of the valve if it needs to be lapped. Your problem sounds to me that the spring is not "springee" anymore. The spring is what sets the pressure at which your valve opens and closes. I am assuming that the valve is not adjustable therefore you need to replace the spring with a new spring. Keep in mind the spring may be color coded as this will tell you what pressure they will operate the valve at. Good luck.

Guess I should read the thread before replying..... As I stated before the seat and disk have different angles. You need to inspect the seat to see if you see any defects in it. This can be caused by erosion of the seat or a foriegn material that got lodged in the seat. If there are defects than i suggest you either lap the valve or cut than lap the valve seat. Make sure the cutter and or lap is at the proper angle for the seat, locally make one if you can. Inspect the disk. If there are any defects on the disk than replace the disk. Than perform a blue check with the seat and the disk. this is where you will see a continuos concise contact ring around the seat. If you dont than there are defects on the seat or the disk. That is where lapping will take care of unless the disk is warped, than your back at replacing the disc. dont ever hit the disc into the seat. This will only cause more damage and you might have to just replace the valve altogether.

Hello

If you need I will try to arange your valve problem solving in our workshop.

Kind regards

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AMares@Petrotel.LUKoil.com