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can then proceed either to the discharge port through channel A or back to the
inlet side of the pump via the bypass channel B and the pressure regulator
assembly (4).
1.3.3 Normally, the constant-displacement pump delivers more flow than the water
outlets connected to the system require. The excess pump flow is recirculated
through the bypass channel and is used by the pressure regulator to set the
pump discharge pressure.
1.3.4 In the pressure regulator, atmospheric pressure and the spring (5) act together
against piston (6), and are opposed by the force of the water pressure acting on
the opposite side of the piston. The spring (5) is adjustable externally by means
of adjusting screw (7) and locking nut (8), and the space behind the piston is
vented to atmosphere through the vent hole (9). Thus, the pump discharge
pressure is set with reference to the ambient air pressure by the spring (5), and
is relatively insensitive to changes in the water pressure supplied at inlet port
(1).
1.3.5 Proceeding along channel A to the water outlets, the useful portion of the pump
flow first passes check ball (10), which is forced back against opening (11) in
sleeve (12) by the flow. To get past sleeve (12) it must compress spring (13),
allowing piston (14) to move back. The force of spring (13) causes a pressure
drop of approximately 5 psi (0.35 bar) to occur at this point. As a result, the
system pressure beyond this point, including the pressure switch cavity (16), is
depressed approximately 5 psi (0.35 bar) to occur below that set by the pump
bypass pressure regulator (4) when there is flow to the water outlets connected
to the discharge port (22).
1.3.6 When flow to the water outlets diminishes, the piston (14) is moved by spring
(13) to restrict the flow past ball (10), thereby maintaining the pressure drop of
approximately 5 psi (0.35 bar) as before. This condition holds, even though the
flow is reduced to a trickle. However, when the flow stops completely, the fit
between the end of piston (14) and the face of seat (15) is not good enough to
maintain the 5 psi (0.35 bar) pressure drop at no flow. Then, with the pump still
running, the pressure in the passages beyond the check ball assembly begins to
rise, approaching that set by the pressure regulator (4). This increase in
pressure against pressure-switch piston (17) causes the piston to rise further
against spring (18), disengaging cam (19) from lever (20), allowing switch (21) to
open and de-energize the motor driving the impeller (3).
1.3.7 As the impellers (3) come to a stop, slight backflow occurs because the impellers
in their housing fit imperfectly. The backflow allows check ball (10) to seat firmly
on seat (15), holding pump discharge pressure in the system and maintaining
the switch (21) in the off position.
1.3.8 In any sealed liquid system there is always danger of an increase of pressure
due to temperature changes, etc. A pressure relief must be provided. This relief
PO Box 8975, Vancouver, WA 98668-8975 • Phone: 360/253-2008 • Fax: 360/253-8294
2 Howard Road, Eaton Socon, St.
MICROPUMP, INC.
A Unit of IDEX Corporation
MICROPUMP
A Subsidiary of Micropump, Inc.
Neots, Cambridgeshire, PE 19 8ET England, • Phone: 011-44-1480-356600 • Fax: 011-44-
356300
Page 8 of 33
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1480-
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