Erratic Pressures

Eddy

I've got a 2 loop hydronic system. The primary circs the boiler loop and the secondary circs the building loop. They are tied together with a 3 way mixing valve. The valve modulates for a constant 140 deg return to the boiler (cast iron sectional). Static fill pressure is 12 psig. When the system runs the pump pressures are anywhere from 10 psig to 50 psig on the suction and 25 psig to 70 psig on the discharge. The boiler's operating pressure is 50 psig. So, the safety valve on the boiler dribbles when the suction gets near 50 psig. Why aren't my pressures more constant? It does not appear that the position of the 3 way valve has any affect on the pressures. I have the same problem with the chiller loop which also has a 3 way valve for the cooling coil.

Are my compression tanks (bladder type) not working or maybe plumbed wrong?

[Deleted User]

Assuming the job

is piped correctly - it sounds like the valve(s) CV is not matched to the pump(s) capacity. I would get out the specs for all pumps & valves & give them a double check.

thp_8

okay

Please give us a cheesey little drawing of the piping layout.

Dale

Burner off

I would check pressures with the burner off and the static starting at 12 psi on all the gauges. I would make the pumps run and see what the pressures are with no heat. If they go up as you say you must have pumps with tremendous head. If they don't then you have a air cushion issue in the expansion tanks.

Eddy

That could take me a few days but i'll give it a shot.

thp_8

be waiting

thanks