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mfqd (Mechanical) (OP)
20 Jul 09 13:41

When coosing a 3-way valve, how can we decide between mixing or diverting valves? What are the reasons to choose each one. Wich applications are they mos suitable for?

hydtools (Mechanical)
20 Jul 09 14:39
A the valve description '3-way' means the valve has three ports.  You decide if you want to divert one input to one or the other ouput or if you want to combine two inputs into one output.  If you want to divert one input select the diverter valve.  If you want to combine two inputs select the mixing valve.


TD2K (Chemical)
20 Jul 09 22:02
What's the application as that could definitely set what factors you want to consider.
TD2K (Chemical)
20 Jul 09 22:07
I'll add that a current job I'm working on uses 3 way valves to control the flow of fluid to a heat exchanger.  That's the first time I've seen them used in what I call process applications.  I have seen them used in auxilary services.  For example, 3 way valves are not uncommon in lube oil services to maintain a constant oil temperature by bypassing some of the hot oil around a lube oil cooler.

When we talked to Fisher their first comment was 'why would you want to use 3 way valves?' smile
quark (Mechanical)
21 Jul 09 3:35
With about 13 years experience in HVAC and process cooling applications, I have yet to find out a logic for either to use mixing or diverting valves. Both can be used for either flow control or temperature control application with out any problem and there is not extra benefit if you choose either one. However, the selction is cirtical with respect to the location of control valve and that is all.

If this is for a heat exchanger application (as I understand from your other thread) then 3 way valve is a kind of dead duck. I replaced many three way valves (or blinded one port) with two way valves. Don't let your pump gulp more energy when it is not required.

mfqd (Mechanical) (OP)
21 Jul 09 6:16
Thanks for the replies. I think i understood perfectly!

I'm more calm now that i eared from you that there is no special reason to choose between both. For what i understood, it depends on the application and if it's possible is better to choose a 2 way valve.

Thanks! If there is any more arguments that you think that might be interesting, please reply again!

Scotsinst (Petroleum)
22 Jul 09 23:30
One situation where a three-way valve can replace 2 2-way valves is in a heat exchanger series/bypass line to prevent the possibility of line being shut in.
The 3-way valve eliminates the requirement for a liquid safety valve (if this would be an expensive solution).
mfqd (Mechanical) (OP)
31 Jul 09 12:43
Thank you all!

Ok. I understand that id depends on the aplication, and for example if we have the kind of situations exposed by "Scotsinst", we definatly must use 3-way valves.

But, still i have a question regarding this issue of the 2 or 3-way valves, also exposed im my other thread: when using a 2-way valve, there are changes in the flow rate, and consequently in the fricton losses. This induces some kind of dynamic behaviour in the system with implications on the pump.
My question is: how is the pump dimensioned in this case?


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