3 Way Valve Discussion

Unknown

Mixing valve has 2 ins and 1 out, diverter has 1 in and 2 outs. That's just old school.

hvacfreak

3 Way Valves

I spend more than a few days each week re-piping three way valves. I work for a mechanical contractor that has many mechanics that don't seem to get these right. And yes , I do understand the confusion ...the paperwork is intended for the control wiring technician , not the pipe fitter.

I'm kind of in the middle and from "MY" perspective I say that some brands make it more confusing than it needs to be. I have to give credit to Belimo on that statement as they seem to attempt to explain this better than any of the others in thier O & M's.

AB-A-B , Com.- N.o - N.c , mixing , diverting , CV , 1 arrow , 2 arrows...there is no standard and directional arrows don't always indicate fluid direction. Convoluted BS I say.

CV...ok , 6 inch welded CHW piping reducing to a 2.5 inch valve and increasing back to 6....so , the 6 inch pipe is oversized from the begining...2 1/2 inch should be fine throughout. The math for piping is different from the math for the valve...WHY ? 2 1/2 pipe would at least be acceptable for a duration...but this is not stated.

Counter flow and parallel flow....where would " counter flow " not be the best option ? Why is this not a " standard " . Commercial AHU / coil modules or units are not always tagged ( or submitted ) in / out or supply / return...why not always pipe counter flow ?

All of this gives me work to do , so..." that don't befront me , as long as I get my money by next Friday ". But yeah , I'd like to others thoughts on the issues I've mentioned , for conversation if nothing else.

bob_46

Opinion

First, the superintendent on the job should "get his money". Second, I believe the cause is not with the valve mfg. or the engineer. The draftsman drawing the print has no way to know what make valve the contractor will supply. He draws the 3-way so the piping "on the print" is as neat and easy as possible. It is the installers responsibility to "insure" that the valve is correctly installed. Third, do you size a pump by flange size, or a boiler by taping size? Why would you size a valve by pipe size? Fourth, is the fitter responsible for the engineering? I realize it is a PITA to repipe a 3-way, usually after you screw a few up and have to change them you learn to never assume the ports are the same as the print. Regards bob

hvacfreak

I agree..on most...

...of what you say...but the " dramatic" difference as described by the valve manufacturers and the controls subcontractors conflict GREATLY with our pipe sizing ( or the mechanical engineers at least ). After restance of piping and size , what else is left ? The reduction minus the restance becomes the " flow ". 6 inch to 2 1/2...hell , lets run 3 inch and call it a day....it has to be the same.

hvacfreak

sure

That is an answer to a part of the delema , thanks. And how about " normally closed " on a " floating point 4 to 20 MA trick " ?

Unknown

NC 4-20

I a control system that calls for a NC valve, normally the control signal from the controller would be 4MA closed and 20 MA open unless it is wired reverse logic for a freeze protect application.

hvacfreak

funny you mention that

I brought this up on a recent repipe...I was asking for the RFI replies...I said...what can a 3 way valve do that a two way valve can't if there is no circulator involved...the correct answer is " nothing " , short of constant flow regardless of demand ( constant call for heat. And we get back to the original statement ... " convoluted ".

hvacfreak

residential vs commercial

In my travels , at the end of the day ( yeah , thats overused ) ...most folks on this board understand fluid dynamics ( or at least flow ) much better than the " educated " people I encounter in schools and office buildings.

You know , I am paid well for translating BS. I say I'm a " dullard " with great reading comprenhension..I 'm not great nor even close to it. I just understand the " doublespeak. A professional bser.....great.

edit : clarification...I am paid to defend , nurture , cultivate ...****....3 way valves and thier control are always a paradox , resulting in relief valves blowing off and frozen coils in commercial ahu's. Engineer's act like they're the first to do any of this....fookin amazing.

jeff klaverweiden

I have installed a few in backwards, then I read in the instructions [ab] is common to both. Then it made sense.No matter what position the valve is in I need flow through AB. So in bypass or through the coil AB is always part of the circut. We always have Heat is fail to heat and cool is fail to bypass

Paul Pollets

Mixing valves

we just fixed a project where the mechanical engineer specified 4 way valves and piping oversized by 300% in seven buildings. The pumps were also 300% oversized.


It's not uncommon to see the devices sized wrong or installed improperly. What else is new?



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hvacfreak

sure

If you don't understand the design intent , your still dead in the water.

Lets say that you have a Siemens valve ( 3 way ) with an arrow ( 1 ) pointing through the body. It is listed on the contract drawings as a two way valve but an RFI has run it's course. You are in building 2 of 3 that are served by the same heating plant. No updated drawing is given , only a written directive stating to provide a three way valve ( like **** ).

I repiped this as " mixing " ...open to the coil on a call for heat , bypass through the main when not.

No , NC ( while modulating ) ...mean nothing...might as well say normally maybe , normally maybe not. and either may apply at any instance. Convoluted BS.