Does it really matter?

[Armaton]

Since I have a closed pressurized system, does it matter where in the system I put the hydraulic separator make up pump? Such as in barn next to storage and "Push" water to house, but would require another wire be run to barn from the controller. Or, in the house, (more convenient), and pull the water to it?

 

[ewdudley]

It doesn't matter until you have cavitation. Everybody warns against too low a pressure at too high a temperature, but it's hard to find hard limits for specific pumps.

Ideally you could move your expansion tanks to the house where you want the pump to be.

But since your pump won't be developing much over 4-6 psi of head, and the pump will be roughly at the midpoint of the loop, which means there will only be 2-3 psi of pressure drop from the expansion tank to the pump, and your system is pressurized, it probably wouldn't hurt just to go with the pump in the house and if you suspect cavitation as evidenced by a noisy pump you can push the system pressure up higher and if that don't work you can look into moving the expansion tank or moving the pump, having planned for the latter eventuality.

(I have a 007 in the house, 50 ft away from the expansion tank, and pulling through 50 ft of [nominal] 3/4" PEX, with typically 180 degF water, and a system pressure of 15-25 psig with no evidence of cavitation.)

 

[Armaton]

Eliot,

If you remember my system design, I have my expansion tank hooked into the near boiler loop between my storage and LK 810, so moving it to the house really isn't an option. If I did get cavitation, would adding a smallish bladder expansion tank just before the pump in the house fix the problem?

 

[ewdudley]

If I did get cavitation, would adding a smallish bladder expansion tank just before the pump in the house fix the problem?

I think it would help, but I don't know how much. Intuitively you would have exactly half the pressure drop at the inlet to the pump than if there was one tank at the halfway point at the opposite side of the loop.

But not to worry. Assuming your house loop is designed for something like a 008 and 12 feet of head, as opposed to a 009 and 25 feet of head, I don't think you will have enough pressure drop on the inlet side of the pump to worry about cavitation.

And even if you did have a pump that developed 25 feet of head, that's a pressure drop of only about 6 psi at the inlet of the pump half way around the loop away from the expansion tank. If your system was filled to 13 psig static the pump would still see 7 psig at the inlet while running, still decidedly high enough not to worry about cavitation. And even supposing I'm wrong andf there was cavitation, you could likely cure it by filling the system to run up closer to the relief pressure of the boiler.

 

[Armaton]

15-58FC pulling through 130 foot of 1" pex. Should be good! Fingers crossed.