Response
to E-mail Question
August 4, 2003
Dear Ken:
I’ve highlighted the words that specifically
exclude mechanically actuated diaphragm pumps in this specification. These are often
referred to as MAD pumps. The hydraulically backed diaphragm pump is an old design, and is
most useful for high volume/high pressure applications. When boiler chemicals were all dry
products that required dilution with water to feed them, and a tank/tank
stand/mixer/bottom mount platform with a high volume pump to feed the dilute chemical
directly into a high pressure boiler, then this style of pump was the norm. Now, however,
it is more common to feed a neat, or concentrated chemical to a low pressure boiler or
de-aeration tank. The hydraulically backed diaphragm pump can’t feed really high
volumes (municipal size), and there is seldom a need for really high pressure other than
for a limited number of very large boilers.
MAD pumps are capable of high volume at relatively low pressure (100 to 150
psi), which is usually adequate for municipal jobs. Solenoid pumps are used most commonly
for neat boiler chemicals now, feeding at 150 to 250 psi.
A specification intending to exclude hydraulically backed diaphragm pumps would
emphasize a pump that did not include the "lost motion" design principle
(presumably because bypassing hydraulic fluid internally wastes energy), and one that
stresses the importance of a direct mechanical connection between the motor and diaphragm.
In reality, any of these pumps can work just fine if they are selected to match the needs
of the particular application. I tend to prefer a selection process that evaluates the
customer’s short and long-term equipment capital and maintenance costs.
Please let me know if this answers your questions about the basic difference
between the two types of pumps, Ken.
Sincerely,
Tim Furrow |
