Condensate tank

exqheat

If a condensate tank is located below the level of the boiler, should there be a back-flow check valve on the feed to prevent condensate from coming back to the tank when the pump is not active. It seems the water elevated in the boiler will push back through the pump to the tank, when the boiler is at proper level for heating. This becomes a waste of electrical pumping energy, a shortening of the life of the pumps. If the boiler is shut off the pumps are off, and the water will be wasted off the tank overflow. Two choices: Raise the condensate overflow pipe to the level of the proper water level in the boiler, or install a check valve. The benefit of the raised overflow pipe drain on the condensate tank would avoid the problem of overfilling the boiler. This would not reduce the flow back and inefficiencies caused by the lack of a check valve on the feed side.

Your thoughts are most appreciated.

ScottSecor

As far as I know, all steam condensate tanks should have a check valve on the pump outlet. Otherwise the boiler water would back into the tank often and flood the tank.

JStar

No matter where the tank is located, you should install a check valve on the discharge line.

JUGHNE

Without the check valve the pump would continually cycle as the water flows back and is pumped out again.

A pump cycling like this when no water is returning is a symptom of a failed or non sealing check valve.

exqheat

On second look, it appears that there are two check valves, but they must have failed. The pumps are running every 5 minutes. The ck valves need to be checked cleaned or replaced.

Pumpguy

It would be a simple matter to close the ball valves on the discharge lines. If the cycle time increases, the problem is leaking check valves.

If there is no change in the cycle time, the problem is somewhere else.

EBEBRATT-Ed

@exqheat

If I am not mistaken ASME CODE requires 2 check valves 1 at the boiler and 1 at the pump.

What you described is a common problem.

I have also had the reverse be true.

I replaced a boiler where the new water line was lower than the old boiler, making the water level in the feed tank higher than the boiler.

The problem was once the pump ran the first time it started a syphon and all the water in the condensate tank ran into the boiler. There were 2 fixes for it. Install a motorized feed water valve or (the fix we used) was run the feed water pipe up over the new boiler and install a vacuum breaker at the highest point

exqheat

I'll try the valve shut off test.

exqheat

My detection was that after a pump cycle, the water would warm up as if the water was coming back from the boiler. If I close the ball valves, how does that check the check valves. There would be no water flow. When the pumps run the water in the boiler glass goes up. The water glass then shows the water lowering over a short time. The addition of a water meter to the feed would tell me more if there is a water loss occurring in the returns?

Jamie Hall

Seems to me you've proved your case there. I'd probably replace those valves...

Lard

I have had this exact issue. The check valves are shot (likely full of crud).

Replace them with a good quality unit, not the cheapest available. I like using Y-pattern swing checks as they tend to have fewer seating issues/better longevity.

EBEBRATT-Ed

@exqheat
What @Lard said

ScottSecor

I agree with @Lard . Replace the checks and eliminate one problem

dopey27177

The check valves on the discharge side of the pumps must be spring loaded check valve.

Swing checks can slam closed, additionally they wear out much faster than spring loaded check valve which are designed for pump usage.

Jake

exqheat

I will have to determine if the returns are leaking. That will be helped by adding a water meter to the feed line.

exqheat

Thank you all. Very helpful.