This week let’s talk about the evolution of Auto degassing
heads. At one time the introduction of
the integral bleed valve was thought to be revolutionary. And while it greatly assisted in the priming and operation of the pump, it wasn’t a true fix to being able to handle fluids that
off-gas because it still requires an operator to see that the pump has vapor
locked, and then open the integral bleed valve to purge off the gas.
(Integral bleed valve indicated)
What I
consider to be the auto de-gassing head, is the one with 3 ports; one on bottom
(suction), one out the back (discharge), and one out the top (vent).
First time users of this pump will often pipe it incorrectly
as they will assume the top port is discharge and the one out the back is the
vent. However, that is switched, and for
good reason. These pumps are designed so
the gas will rise to the top port and get continually pushed out. The downside is that some fluid will
naturally get cycled out the vent as well, thus these pumps must be de-rated in
order to more accurately establish their likely flow rates. The fluid is then
discharged out of the port configured out of the back of the pump in a
horizontal manner. This style pump has
greatly improved the dosing of chemicals that off gas.
In recent years, some manufactures have begun to automate
the, previously discussed, bleed valve portion of the pump. The
pump is designed to be able to notice when there is air in the head of the pump,
and a relay then causes a solenoid to open the bleed valve. The pump then goes to max frequency and the air
gets purged through the pump during the pre-set timed sequence. The pump can be programmed to operated this sequence as a preventative measure, or corrective action. This has proven to be a pretty effective yet costly addition, as it requires an additional solenoid, the use of a relay, and a dedicated panel. Yet to correct or prevent the
headaches associated with vapor locking your pump, is often worth that additional price.
Next time we’ll talk about the newest manner in which
metering pumps are passing gas…
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