1
Instruction Manual
1.1 DESCRIPTION
Milton Roy Pneumatic Actuators are an accurate
and convenient capacity control device. They are
ideal for plants which currently employ pneumatics
or which need automatic explosion proof pump
capacity adjustment. An optional air control station
can provide local or remote manual adjustment and
an auto / manual selector valve when required.
1.2 PRINCIPLE OF OPERATION
1.2.1 Major Components
Figure 2
illustrates the physical relationships of the
parts and subassemblies described below.
Basically, the operating principle of the Pneumatic
Capacity Control is similar to a conventional
pneumatic valve control, except the regulated
supply air pressure (metered by the Moore Valve
Positioner) is used to pressurize the oil reservoir
which transfers the oil to the back of the Actuator
Piston (1150).
Major components of the Pneumatic Capacity
Control are:
1. The Actuator Piston (1150) is connected to the
pump gear housing and moves to establish and
maintain the pump capacity.
2. The Oil Reservoir (1290).
3. The Transfer Shaft (1220) connected to the
Actuator Piston(1150) to transmit the piston
position to the Range Spring (1420) in the
transparent plastic cylinder (1430).
4. The Moore Products Valve Positioner (1440)
monitors the Actuator Piston position as a
function of the applied instrument air signal
and develops the necessary metered supply air
pressure required to reposition or maintain the
position of the piston.
1.2.2 Operating Description
The Actuator Piston incorporates the differential
area principle with the supply air pressure
(80-100 psi) (551-689 kPa) applied directly to
the small area of the piston. This establishes a
constant preload through the piston transfer shaft
and range spring to the Moore Valve positioner.
Hydraulic pressure is not used on the preload
side of the actuator piston, since the pressure is
constant and the hydraulic snubbing effect is not
required in this direction.
In order to move the Actuator Piston in both
directions, the force on the opposite side of the
piston must be variable to a higher and lower value
than the preload force developed by the supply
pressure acting on the small area side of the piston.
The Moore Valve Positioner compares the applied
instrument air signal with the Actuator Piston
position, as indicated by the range spring force,
and adjusts the air pressure applied to the oil in
the reservoir. Since the oil reservoir is connected
directly to the large area side of the Actuator Piston,
a force proportional to the oil pressure is obtained.
This force opposes the fixed force caused by the
supply air pressure on the small area side of the
piston.
SECTION 1 - DESCRIPTION
