Boilers and pressures 5

[clubhouse]

Can any body tell me how to lower the water pressure in a closed loop boiler system? This is a RAYPAK system, suction side of the pumps is sitting at 27 psi and discharge is at 70 psi and at the boiler inlet is at 27 psi and the out side is at 56 psi, and the blow off valves are rated for 60 psi so I am getting blow offs to frequently because the difference of 4 psi coming of the boiler I believe is to close.

Thanks.

 

[willard3]

I'm surprised that the boiler is 29 psig....have you checked this with the boiler MFG?

This seems awfully high pressure drop for a boiler.

 

[RossABQ]

Reduce the make-up water pressure regulator setting (near the expansion tank), and the pressure on the bladder. They set the pressures throughout the system. You might have to bleed off a little water initially .

 

[cme]

calculate the pressure from the static height of the highest point to the expansion tank then add 3 psi

you should also be pumping away from the boilers

the expansion tank is connected to the suction side of the pump via the air separator (rolairtrol)

b&g has a program to calculate expansion tanks .... there is a formula in the code books

 

[kenvlach]

Is the problem with the internal circulation pump in a HW boiler? If so, this should be handled by the mfr. If an external pump, please tell the model & layout of your system. Raypak has all sorts of technical info:

http://www.raypak.com/commframe.htm

 

[willard3]

snip
you should also be pumping away from the boilers
snip

This is another piece of accepted wisdom that doesn't make any physical sense. If you pump through the boiler, you raise the pressure and hence the boiling point....the opposite is true if you pump away. You just have to recalculate the zero-pressure point to place the expansion tank, but that should be done anyway.

Bell and Gosset shows pumping away from the boiler and offers no explanation and it becomes law....poop on that

 

[TBP]

The main reason for pumping away from the boiler is to better facilitate dissolved air removal. Install the air separator just after the boiler and right before the pump. Located there, the separator will see the hottest water at the lowest pressure, meaning it's closer to the boiling point than anywhere else in the system. Being closer to the boiling point, this is where any dissolved air will tend to pop out of solution. And the separator is right there, to grab it.