H. Hydraulically Backed Diaphragm Pumps
This pump is characterized as a lost motion device, because its
output is controlled by a variable oil bypass. While the design itself is somewhat aged,
there is really no significant difference between the operation of this type of pump and
that of a mechanically actuated diaphragm style of pump. One advantage of this pump is its
ability to produce high pressures (1,000 PSI+) although that capability is needed less and
less these days. Cost and low end performance are drawbacks.
M. Mechanically Actuated Diaphragm Pumps (MAD)
A direct coupling between the motor and pump diaphragm defines a
MAD pump. Like gear and hydraulically backed pumps, DC motors are often employed to work
with proportional 4-20 mA DC signals. In the mid-range pumps, however, there have been
some recent breakthroughs in modulated AC drives, which significantly improve their
overall economics. These pumps tend to prime readily in suction lift applications, even
though they perform best with a flooded suction. They work well in municipal-sized jobs.
P. Peristaltic Pumps
These pumps squeeze the products they pump – sort of like
compressing and pushing to do the pumping. As a result, they are good self-primers, even
though they fall down at high pressure or high output. Their maintenance frequency can
also be a drawback.
S. Solenoid Pumps
This last pump has been increasingly used to pump neat, or
concentrated, chemicals. Being able to control both the stroke frequency and stroke length
allows these pumps to operate over a very broad output range. In addition, within their
range, they are very accurate and easily controllable. All of this and good economics has
produced an increase in their use during recent years.
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