Skidmore Condensate Pump capacity

JUGHNE

I have this older pump doing part of the capacity of a system. If I could add 2 dry returns which are trying to drain into the discharge of this pump I believe this would solve delayed return and flooding/overfill of boiler at end of cycle.

The Skidmore web site does not show the EDR capacity for this model number: 56948-1S, Date code K90X, Shop order 68,622 S. The cast iron tank is 15.25" long, 8.5" wide, and 16.75" tall. No legs, 1/3HP 120 VAC. Switch on top.

The smallest in the newer literature is XC2S61....1/3 HP.....6 gallon....rated 8000 EDR.

Now, dumb and probably obvious question: the 8000 EDR referred to is the connected radiation EDR amount of returning condensate???

Thanks.

Pumpguy

First of all, PUMPS DON'T HAVE EDR, RADIATION DOES. Expressing pump capacity in terms of EDR is a pet peeve of mine, especially when it comes to vacuum pumps, but unfortunately, that's the way the industry does it.

The issue is, different manufacturers will offer different pumping capacities for a given EDR load. So you should first know your EDR load, and then calculate the needed pumping capacity.

For condensate pumps, most will size the pump based on 3X the condensing load, but in practice, 2X the condensing load is adequate. So what you need to be concerned about is the needed pumping capacity and receiver tank volume based on the EDR load you actually have.

Typical pumping capacity for a 1/3 HP, 3450 RPM condensate pump is 15 GPM @ 20 psi.

Standard receiving tank sizing is a one minute storage capacity. This means that based on a 6 gal tank size, the pump would be rated for 6 GPM, but the impeller and motor should be able to move the 15 GPM @ 20 PSI.

Ultimately this will depend on the trim of the Impeller OD. Based on information I have for other brands, @ 3450 RPM, a 3" impeller is used for 10 PSI service, while a 3.5" impeller is used for 20 PSI service.

What you really need to be concerned about is the cycle time. Based on the one minute storage capacity standard, I would be comfortable with about a 45 second pump out time. Of course this will depend on the settings of the float switch, which can be adjusted. The off cycle will depend on how much condensate is flowing into the receiver, and how closely the receiver volume is sized to the condensing load.

JUGHNE

Thank you Pumpguy! Good informational and educational reply. The building is a 1938 school that is due for demo in the next few years. Hardly 30% of the building is used.

I want to add 2390 connected EDR to this pump. Can't say what is connected to it now. I now have the valves off on 2 large air handler steam coils. They each were fed by 2" supply coming from a 3 1/2". Each had a 1" F&T. So that condensate load is gone.

My gut feeling is that the pump can handle the new 2390 load. I also have the ability to reduce the connected load with orifices if need be.

The existing load causes the pump to run maybe every 10 minutes for perhaps 10-15 seconds.

The smallest Skidmore pump is rated at 8000 EDR. The smallest Hoffman is rated at 6000 EDR.

Pumpguy

2390 SQ Ft EDR will add 2.6 or 3.9 GPM to the load, depending on weather you use 2X or 3X the condensing rate. So, it depends on how much more condensate this unit has to handle to determine the overall suitability of the existing pump.

With a cycle of OFF 10 minutes and ON 15 seconds, looks to me like you have plenty of capacity available.

JUGHNE

Thank again, Pumpguy. I think I will go with it and just shut down some radiation if need be. It is easy for me to over analyze problems, but you have to just do it sometimes and always say it should have worked.

This system has only 26" of "B" dimension trying to get dry return water into a wet return with Hartford Loop on a 52 HP boiler running at 2.25 PSI. Also the cond pump in pumping into the wet return on it's cycle.