2
Instruction Manual
SECTION 1 - DESCRIPTION
The mechanical drive system of the pump drives
the plunger back and forth in the High Performance
Diaphragm (HPD) liquid end supplied with the
pump. At the start of a suction stroke, the plunger
moves away from the liquid end, drawing hydraulic
fluid with it. As the hydraulic fluid is drawn back,
the flexible diaphragm (510) follows, lowering the
pressure of the process fluid in the liquid end.
This pressure drop causes the ball(s) in the suction
check valve
(Figure 10)
to be lifted up thereby
allowing process fluid to pass through the suction
line into the diaphragm head (1020). At the same
time, the pressure drop in the diaphragm head
causes the ball(s) in the discharge check valve
(Figure 10)
to be pulled closed, blocking flow back
through the discharge line.
Note:
It is important that the pressure in the liquid
end remain above the vapor pressure of the
process fluid during the suction stroke. If the
fluid pressure drops below the vapor pressure,
cavitation will occur, negatively impacting the
performance of the pump. If you suspect the
possibility of cavitation, contact your Milton Roy
Representative for assistance.
At the end of the suction stroke, the process
reverses, beginning the discharge stroke.
Now the plunger moves forward, pushing hydraulic
fluid before it. The hydraulic oil must therefore press
against the diaphragm, flexing it forward and raising
the pressure of the process fluid in the liquid end.
This pressure increase causes the process fluid
to flow outward, forcing the discharge ball check
open and the suction ball check to seat, blocking
back flow through the suction line. The process
fluid flows out of the diaphragm head and into the
discharge line. This suction/discharge action is
repeated with every stroke of the pump plunger,
and is the direct cause of the pumping action.
As the pump operates, a small quantity of hydraulic
oil is continuously bled through the air bleed system
(970, 960, 980 in
Figure 8
) in the three- function
hydraulic valve (air bleed/relief/purge-
Figure 8
).
An additional small quantity of hydraulic oil is
also lost on every stroke through the clearance
between the plunger and displacement chamber
bore. After a while, these normal losses result in
a shortage of hydraulic oil in the displacement
chamber. When this happens, the diaphragm will
be pulled back tight against the back contoured
surface of the displacement chamber, and part of
the diaphragm will press against the Mechanically
Actuated Refill System (MARS) valve
(Figure 9)
.
Now, when the plunger draws back, a vacuum is
created in the displacement chamber. These two
factors (diaphragm pressing against MARS valve &
vacuum in the displacement chamber) must occur
together to trigger the MARS valve.
When both of these conditions are met, the MARS
valve is forced to its rearward position, and the
poppet (760) opens, allowing hydraulic oil from
the reservoir to enter through the refill valve
(740 in
Figure 8
) and replenish the lost oil. In this
manner, proper hydraulic balance is constantly
maintained in the displacement chamber.
