# Triple duty valve question.



## Crazy (Jul 4, 2013)

Putting together a mechanical room with chillers and pumps, no boilers. For the cooling tower water, it's a 3 pump system, we're just putting the stacks up right now. 8" pumps, after it 90's up we go to 10". Short flex, then Tr D valve. (now tr d's are 8 foot off the ground, can't read the stem!) Then reduce again, back to 8" until it ties into the 14" overheads to go out to hospital. It sure looks strange seeing 10" tr d's in an 8" line. It is what the prints call for, and it's what they're getting. 

Not gonna change it, just getting opinions. I don't see the need for a 10" tr d in an 8" line.


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## wyrickmech (Mar 16, 2013)

Your output of the pumps is restricted by discharge pipe size to a point the ten inch triple duty is oversized. The only reason I can see is that maybe the flow rate was so close to wide open that for balancing reasons they up sized the triple duty to bring the flow rates to a lower setting on the valve.


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## dclark (Dec 12, 2010)

*tdv*

Not sure what brand you're using, but they should all be close

Look at the difference of the performance curves.. pick 8" and 10" with a 5psi pressure drop.. 8" is about 1800gpm, 10" @ gpm3000

http://www.wattscanada.ca/pages/_products_details.asp?pid=543

Resources tab.. look at either one of the pdfs
Hope that's what you were looking for

Regards


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## Crazy (Jul 4, 2013)

While we use WATTS for our plumbing needs, especially backflow preventers, we use Bell & Gossett TDVs and pumps. What I was really wondering about was the double size change. I know it is what they are asking for, but going from 8" to 10" to put in a 10" TDV, then reducing right back to 8" for the run to the main 14". Isn't any benefit for the larger tdv cancelled out by going back to 8"? 

Thanx. Crazy


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## plumbing ninja (Jan 15, 2012)

All relative to the flow rate duties! 
I would probably leave an 8" flange set with a 1/8" spacer downstream of the TDV!
This is so you can fit an orifice plate in when they finally conclude it's all been oversized for the actual duty! They'll discover this 2 yrs later


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## Crazy (Jul 4, 2013)

plumbing ninja said:


> All relative to the flow rate duties!
> I would probably leave an 8" flange set with a 1/8" spacer downstream of the TDV!
> This is so you can fit an orifice plate in when they finally conclude it's all been oversized for the actual duty! They'll discover this 2 yrs later


There is an 8" flex below it, flanged, and a reducer above it, flanged. It would be no trouble to change it out later, just make a custom spool and switch it out. I just want to know he reasoning for it. No matter how good the flow rate, reducing back to 8" ought to curtail it. Why it was designed so high off the floor seems ludicrous to me as well. But I just put it in, not design it. And there is no room for any adjustment, they want it exactly like it is.


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## Crazy (Jul 4, 2013)

dclark said:


> Not sure what brand you're using, but they should all be close
> 
> Look at the difference of the performance curves.. pick 8" and 10" with a 5psi pressure drop.. 8" is about 1800gpm, 10" @ gpm3000
> 
> ...


I re-read your post a few times, and it makes sense! An 8" , wide open, with the obstructions the valve stem and head puts in the line, would render it less than prime 8" flow. A 10", minus the valve assembly obstruction, would be close to 8" with no obstruction. 

It makes sense. If the valve is needed to be 100% open, it would flow like an ordinary 8" opening. Cool deal! An 8" valve, open %, would still be less than 8" in flow rate. Makes sense............I shoulda thought of that....

Thanx. Crazy


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## rjbphd (Feb 5, 2010)

I'm the one going crazy here, what the hell is TDV??? Thanks


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## Crazy (Jul 4, 2013)

rjbphd said:


> I'm the one going crazy here, what the hell is TDV??? Thanks


 
Triple Duty Valve, used in industrial applications......it's a check, flow control and can be (rarely) used as a shut off....mainly used for flow control but the other 2 uses are practical as well. Big , ugly mothers, lol.


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## rjbphd (Feb 5, 2010)

Crazy said:


> Triple Duty Valve, used in industrial applications......it's a check, flow control and can be (rarely) used as a shut off....mainly used for flow control but the other 2 uses are practical as well. Big , ugly mothers, lol.


Thanks.. I'm just a oms working with tidy pipes and fittings..


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## plumbing ninja (Jan 15, 2012)

Crazy said:


> I re-read your post a few times, and it makes sense! An 8" , wide open, with the obstructions the valve stem and head puts in the line, would render it less than prime 8" flow. A 10", minus the valve assembly obstruction, would be close to 8" with no obstruction.
> 
> It makes sense. If the valve is needed to be 100% open, it would flow like an ordinary 8" opening. Cool deal! An 8" valve, open %, would still be less than 8" in flow rate. Makes sense............I shoulda thought of that....
> 
> Thanx. Crazy


I think 10" is oversized! 8" with a smaller valve (2") in parallel would have been better? A control valve should be running about 40-60% open and never at full open. Common to see control valves 1 or 2 pipe sizes smaller but 1 pipe size bigger???


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## plumbing ninja (Jan 15, 2012)

Crazy said:


> Triple Duty Valve, used in industrial applications......it's a check, flow control and can be (rarely) used as a shut off....mainly used for flow control but the other 2 uses are practical as well. Big , ugly mothers, lol.


I've priced these up before and it's always worked out cheaper using individual valves (wafer non return, & triple offset b/fly valve with gear operator) if you have the space?

I think some brands of Triple offset valves even have a buil in filter screen housed in there to offer coarse pre filtering?


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## Crazy (Jul 4, 2013)

plumbing ninja said:


> I've priced these up before and it's always worked out cheaper using individual valves (wafer non return, & triple offset b/fly valve with gear operator) if you have the space?
> 
> I think some brands of Triple offset valves even have a buil in filter screen housed in there to offer coarse pre filtering?


 
We're using 8" strainers with on the incoming side to these pumps, and of course the TDVs go on the outgoing. The B/flys we are using are gear operated too, with chains on the outgoing side.


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## Crazy (Jul 4, 2013)

Its seldom used as a control valve. There is an electric control valve after the tdv that regulates the flow. I think they set theses at roughly 75% and leave it there.


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## wyrickmech (Mar 16, 2013)

Crazy said:


> Its seldom used as a control valve. There is an electric control valve after the tdv that regulates the flow. I think they set theses at roughly 75% and leave it there.


It is a ruff number but it still regulates flow to a point. If there is more than one pump it would be balancing the load more than flow.


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## Crazy (Jul 4, 2013)

wyrickmech said:


> It is a ruff number but it still regulates flow to a point. If there is more than one pump it would be balancing the load more than flow.


You are correct. Once set, they are seldom re-adjusted. The balance pros set it according to the flow, and it is usually left alone after that.


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## wyrickmech (Mar 16, 2013)

plumbing ninja said:


> I've priced these up before and it's always worked out cheaper using individual valves (wafer non return, & triple offset b/fly valve with gear operator) if you have the space?
> 
> I think some brands of Triple offset valves even have a buil in filter screen housed in there to offer coarse pre filtering?


You are talking about two different things one its a triple duty valve two the screen filter is in what we call a suction diffuser they are on opposite sides of the pump.


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