 Please
note that his article discusses a product no longer offered by Domestic Pump. For complete
details on Condensate Units offered by Domestic Pump, click here.A device that has grown in popularity in the condensate return
market is the Pressure Powered Pump. This device was originally called the "Boiler
Return Trap." In two-pipe steam systems the Boiler Return Trap used boiler steam
pressure to put condensate back in the boiler, and it used the water level within the
vessel to operate a float. The float opened and closed two valves. One valve allowed steam
in and the other valve allowed air out. Does the operation of this device sound familiar?
It should, it operates the same as a pressure powered pump.
Pressure powered pumps use the high pressure steam (or high
pressure air) to add energy to condensate. The returning condensate uses the additional
pressure to overcome elevation (static lift) and friction losses. The pump uses 3 lbs. of
steam to pump 1000 lbs. of condensate. Since the PCC uses the energy of the steam to pump
the condensate, it requires no electrical power, and this makes the PCC a perfect choice
for applications where electrical service is not readily available, or in hazardous
environments that prohibit the use of electrical power. In addition, unlike most
centrifugal pumps, the PCC can easily pump high temperature condensate. When installed in
a non- vented application the PCC can pump condensate above 212ºF without flash loss.
While the PCC seems like an easy solution to some difficult
applications, it also requires some special considerations that a typical electric driven
condensate unit does not. The first consideration is filling head. There has to be
adequate filling head (liquid static height) above the pressure powered pump to lift the
inlet check valve. Secondly, pumps using steam as the pneumotive force will not pump
condensate during startup, until steam pressure develops. Third, pressure powered pumps
cannot return condensate to the boiler unless high pressure air is used as the pneumotive
force.
When condensate is collected from a single piece of
equipment, a pressure powered pump can be installed with either a vented receiver or a
nonvented reservoir. However, the non-vented reservoir needs to be large enough for
storage of condensate during the pump's discharge stroke.
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Figure 1 shows an example of a
single source nonvented or "closed loop" application. When condensate is
collected from multiple sources, the pressure powered pump should be installed with a
vented receiver to equalize the different pressures. In a vented application. condensate
from different sources of equipment operating at different pressures flashes down to a
common pressure -- atmospheric. The vented receiver allows the condensate from both high
and low pressure equipment to drain. (If the two devices drained to a non-vented
reservoir, the high pressure device would create a back pressure preventing the lower
pressure device from draining.) |
See Figure 2 for an example of a vented
receiver application.
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If you decide to design a packaged unit around a PCC pump,
here are some suggestions that will ensure the package performs properly.
 Calculate the pumps capacity at the designed filling
head.
Size the vented receiver for the necessary volume to hold condensate during the pumps
discharge stroke.
Size the vented receiver for sufficient cross-sectional area to allow for flash steam
separation from the condensate.
Size the vent on the receiver to allow for flash separation without carryover of the
condensate through the vent line.
The following chart determines the receiver size based on
the volume of flash steam present:
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 Reprinted from TechTalk October 1997
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Article
Morton Grove
Tel 847 966-3700
Taking the Pressure Out of Packaging Pumpless Condensate Units