primary/secondary system

Paul Nebrasky

Recently, we installed a new, "engineered" primary/secondary system. The system includes 5 Teledyne Endurance boilers with multiple pumped zones. The engineer designed a "back up" primary pump into the system. The primary pump(s) are Taco 121's. The zone pumps vary in size but include a Taco 138 on one zone. The system ran fine for a couple of months, then the lead primary pump began leaking, apparently at the water seal. We isolated that pump and turned on the "back up" primary pump. Within days that pump leaked at the seal as well. In my discussions with both the Taco rep and the design engineer, they seem to feel that the system is designed and piped properly. The Taco rep feels that the "back up" pump, which was not isolated, saw back pressure from the lead primary pump. This doesn't sound correct! It also doesn't explain the leak on the lead pump. Could it be possible that the larger secondary pump is having a negative effect on the primary loop. Any input would be appreciated! I have also included a couple of pictures clarify the design.

Doug Wagoner

Primary/secondary piping/pumping

The pictures did not show enough for me to tell if the larger Taco pump was connected in such a way to the primary piping as to have any effect on the primary pressures or flow. Is there any way for you to post pictures of the secondary connections, supply and return, to the primary piping?

Eric

Secondary connections

Check Valve?

Is there a wafer style chk on discharge of primary pump before isolation valve? If not you need one.

Did they flush system and pressure test?

Blow down screen in air seperator? or do you have strainers on pumps. Check them. Air seperator screen are sometime large mesh.

Dont see pressure guages for pump? Take discharge and suction pressure readings on pump and chk where it is operating on curve, dead head pump and check trim. IE on something with this I would think you would have some balancing report.

I like to use same guage and pipe into pump casings