Robertshaw P2 User manual
1
Sales Manual Section 170
PRODUCT SPECIFICATION P2
Side Mounted
Valve Positioner
Model P2
GENERAL DESCRIPTION
The Model P2 Pilot Positioner is a positive positioning relay
for use with pneumatically operated valves and actuators.
This unit positions the valve, correcting for such factors as
stem friction or valve loading by sensing the true stem
position through the feedback lever and utilizing as much of
its independent air supply as is necessary to achieve the true
valve position represented by a 3 to 15 psig (0.2 to 1.0 bar)
instrument pressure.
The positioner is sturdily constructed of aluminum and
stainless steel with Buna-N nylon diaphragms to ensure a
long, trouble-free operating life.
SPECIFICATIONS
Action: ......................................Proportional, Direct-Acting.
Supply Air Pressure:
Nominal ................................................18 psig (1.25 bar)
Maximum ...............................................30 psig (2.0 bar)
Instrument Pressure: .................. 0 to 15 psig (0 to 1.0 bar)
Adjustments:
Throttling Range .................Field adjustable 3 to 12 psig
(0.2 to 0.8 bar)
Start Point ...........................Field adjustable 3 to 12 psig
(0.2 to 0.8 bar)
Repeatability: .........................................0.9% of full range.
Maximum Air Consumption: .............................3.5 SCFH.
GENERAL INSTRUCTIONS
TO BE USED ON CONTROL AIR ONLY. DO NOT
USE ANY OTHER MEDIUM.
1. This positioner will operate properly when mounted
in any position.
2. Do not remove the protective plastic plugs until
just before making the connections.
3. Feedback springs are designed for specific valve strokes
(See table below). If it should be necessary to move this
positioner to a valve having a different stroke, care
should be taken to use the correct spring. Springs may
be obtained from the factory by ordering part number
listed.
ORDERING INFORMATION
Specify:
1. Model Number.
2. Serial Number of Control Valve to
which it is mounted.
VALVE STROKE 1/4" to 3/8"
(6.4 to 9.5 mm)
7/16" to 5/8"
(11 to 15.9 mm)
11/16" to 1"
17.5 to 25.4 mm)
1-1/16" to 1-7/16"
(27 to 36.5 mm)
1-1/2" to 2"
(38 to 50.8 mm)
SPRING 29448-A1 29448-B1 29448-C1 29448-D1 29448-E1
COLOR CODE BLACK NONE ORANGE RED WHITE
2
INSTALLATION
Utilizing the two mounting slots shown in Figure 1, be approximately 1/4 pound (114 g.) load on feedback
bolt the positioner to the valve or actuator. spring when valve starts to move.
Attach the feedback spring, making sure that the Connect the air lines to the proper ports as shown
valve stroke and the spring are matched. There should in Figure 1.
Figure 1
DIRECT
ACTING
TOPWORKS
REVERSE
ACTING
TOPWORKS
Figure 2
3
OPERATION
With the start Point Adjusting Nut (7) at the desired
setting, introduction of instrument pressure creates an
upward force against the Valve Seat Assembly (1). When
the instrument pressure exceeds the downward force of the
Start Spring (8), the Valve Seat Assembly (1) is forced
upward unseating the upper (larger) hemispherical surface
of Valve (2). This opens the passage between the Supply
and Output chambers allowing supply air to flow into the
output chamber and out to the Actuator Diaphragm
Chamber.
The motion of the Valve Seat Assembly (1) is also
transmitted to Pivot (3) acting against Arm (4). This arm
transmits the movement to Feedback Lever (5) which is
connected by a spring to the terminal control valve stem.
Through this linkage, motion of the control valve stem is
fed back to the Valve Seat Assembly (1).
Increasing output pressure moves the control valve stem
downward, increasing the spring force downward against
the Valve Seat Assembly (1).
Rotation of Lever (5) moves Pivot (6) along Arm (4)
thereby adjusting the throttling range of the control.
Therefore, the movement of the control valve stem is
proportional to the instrument pressure change and the
downward force transmitted to the Valve Seat Assembly
equals the upward force of the instrument pressure and both
surfaces of Valve (2) are seated.
Any reduction of the instrument pressure causes an
unbalance, allowing the valve seat assembly to move
downward, opening the lower surface of the Valve (2) and
exhausting Control Valve Diaphragm air pressure until the
control valve stem has moved upward a proportional
amount.
ADJUSTMENTS
Vary the instrument pressure over the range and turn the
throttling range adjusting screw until the desired throttling
range is achieved in stroking the valve.
Then, with the instrument pressure at the desired start
point, turn the start point adjusting nut (Figure 1) until the
valve just begins to move.
MAINTENANCE AND REPAIR
The design of the Model P2 makes routine maintenance
unnecessary.
It is recommended that no field maintenance be
attempted on the device other than replacement of the filter
beneath the supply air connection.
If repair becomes necessary, replace the unit with a new
or factory reconditioned unit.
Figure 3
4
Q-3275 (4/97) Printed in U.S.A.
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