mixing valves

helgy_2

I'm wondering what would be the result of installing a pump pior to the mixing valve in the secondary portion of a primary secondary piping set up. I know that it is wrong, but was wondering why it is wrong. Any help would be great.

Thanks, Helgy.

Mark Eatherton1

Ya mean...

like this?

It has more to do with the pump pumping away from the point of no pressure change more than anything else. I've seen jobs that were done the politically incorrect way, and they work. Pretty noisy, but they do work.

ME

Helgy_3

mixing valves

Actually what I've seen out there is the pump on the inlet side of the mixing valve from the primary loop. What would be the result from the pump at this location. Not good I'm assuming.

Mark Eatherton1

Oh, you mean

THIS way... Ain't no freakin' WAY way.

No, your assesment is correct. It will absolutley NOT work. The 3 way will close it's inlet port due to too high of a discharge temperature. You will then get ZERO flow through the down stream side of the circuit. Even the politically incorrect way is a better way then this way.

If you've seen this, you're guaranteed to get a no heat call. At least you now know how to fix it...

ME

Helgy_3

piping diagram

Thank you for the help. It makes sense to me know. Also I was wondering what program you are using to be able to produce piping diagrams that you are showing me. Would love to purchase such a program.

Thanks, Helgy

Max Frister_3

One pump and mixing valve?

I've got a job coming up where I need a small amount of low temperature water for a supplemental floor radiant circuit. The rest of the system is parrallel, direct return. If possible, I'd like to do it without another pump.

Are there any forseable problems with this arrangment? Mixing valve shown would be a manual one so that it modulates along with the supply temp.

- Max

Arthur

Mixing Valves

Max,
The mixing valve in your diagram will end up just being a diverting valve not a mixing valve. There is no incentive for the water to circulate to the heating circuit unless the mixing valve is closed to return, What happens is the when the valve is say 1/2 open the pump will push into the return reducing the amount of water going to the heating circuit, The water will be still at boiler temp to the first rad or H/E and then because there is insufficent flow the remainer of the rads? will starve of hot water.

Max Frister_3

Proportional reset without an extra pump.

Thanks. So is there any way to acheive this without an extra pump? Will the following location of check valve help establish flow in the "correct" directions?

- Max

Arthur

Mixing Valves

Max, The short answer is no, Suggest you go and read my post again,
The water AFTER the mixing valve has to have some incentive to circulate.
Size the pump on the amount of water (ie the heat loss in the circuit) and the head (ie the resistance of the heating circuit)
The existing pump will have some effect on the 'push' of the new pump when the mixing valve is open,
The circiut needs to redesigned with a separate pump on each heating and the you could get away with out a pump between the header and the boiler although it would operate better with a lo head pump in this postion. In which case the headers need looping together.

Arthur

> Thanks. So is there any way to acheive this

> without an extra pump? Will the following

> location of check valve help establish flow in

> the "correct" directions?

>

> - Max



I enclose a sketch of a suitable setup