valve body hogout model

[thought2007]

Hi,

I have been asked to hogout design of present valve body (cuz in earlier model customer experianced low yield strength of casting ),customer given me requirements of hogout body must satisy all design intents
including flow/pressure drop,material strength & envelope requirements.

What are the precautions i need to take before i start working on this cuz i am new to valve engineering

Is there any good online source to gather more knowledge on valve technology

thanks

john

 

[MikeHalloran]

What is your work product? I.e., are you supposed to machine some valves from billet? Or are you supposed to produce a drawing to do so?

Who has/owns the original design drawings? Do you have any idea what the original design intents are/were?



Mike Halloran
Pembroke Pines, FL, USA

 

[thought2007]

Hi MikeHalloran

Thanks for your quick reply

Well, i am doing designing valve body by considering machining & finally requirement is to make drawings too.

And i have details oil properties,flow rate,pressure drop,leakage

thanks& regards
John

 

[MikeHalloran]

I see a potential problem here. Suppose you design a billet machined valve body fully compliant with the cast body's geometry to a reasonable approximation, i.e. same machined surfaces on interior, machined approximations to cast surfaces on inside, same machined surfaces on exterior, machined approximations to cast surfaces on outside, etc, and you specify a material with properties similar to or better than the cast alloy.

If it turns out that the old valve failed because of a design flaw, not a material flaw, then you have made a machined duplicate of a flawed casting design, and the new valve will fail in the same way as the old one, unless perhaps the new material is substantially better.

This is primarily an artifact of requiring the 'same envelope'. Sure, same overall length etc. makes sense, but especially because an article has already failed, I personally would be inclinded to upsize the stressed parts of the valve, e.g. make the bulk of the body thicker, with larger wrenching features or thicker flanges, all of which is actually cheaper to do when making the valve from billet.

If weight or fatigue is not a huge issue, I'd even be inclined to leave the outside of the body "squared off" to a large extent, because it's cheaper and because it's free strength.

But this doesn't sound like the sort of thing that you feel comfortable doing, which is why you came here. At this point, I'd suggest making a drawing of what you can do to approximate the _interior_ of the cast valve by machining, and ask the customer to take responsibility for material selection and for the exterior geometry, or to engage a third party who can do so. Unless you told the customer that you're a complete valve design house, in which case you should engage the third party.

The way you describe the relationship between you and the customer suggests the faint odor of the remote possibility that he knows the design is flawed, and he's trying to snooker you into accepting responsibility for it, and paying to get it fixed. In which case it would be cheap insurance to engage a third party of your own anyway.






Mike Halloran
Pembroke Pines, FL, USA