azbil VPP 02 Double Acting Pneumatic Valve Positioner User Manual
- June 13, 2024
- azbil
Table of Contents
Double Acting
Pneumatic Valve Positioner
Model : VPP 02/VPP 03
User’s Manual
VPP 02 Double Acting Pneumatic Valve Positioner
OM2-8310-0300
NOTICE
While the information in this manual is presented in good faith and believed
to be accurate, Azbil Corporation disclaims any implied warranty of
merchantability or fitness for a particular purpose and makes no express
warranty except as may be stated in its written agreement with and for its
customer.
In no event shall Azbil Corporation be liable to anyone for any indirect,
special or consequential damages. This information and specifications in this
document are subject to change without notice.
© 2013 Azbil Corporation All Rights Reserved.
DOUBLE ACTION PNEUMATIC
VALVE POSITIONER
MODEL: VPPO2 AND 03
ILLUSTRATION
C. VPP Positioner, Back View with One of Relay Being Dismantled
GENERAL
The Model VPP02/VPP03 Valve Positioner is used to position a double acting air
cylinder, responding accurately and rapidly to the pneumatic signal received
from a controller. Principal constructions are as follow:
PRINCIPLE OF OPERATION
The VPP positioner employs a force balance system. Referring to Fig. 1, when
balancing between the force of the input bellows and that of the feedback
spring is disturbed due to variation of the input fed from the controller or
due to external disturbances caused to the control valve, air to the actuator
of control valve is increased or decreased until the bal- anced state is
restored and, then, provides the valve opening corresponding to the input
signal.
The VPP positioner can be selected either in the direct or reverse action. The
explanation here is made for the case of the direct action. For reversion of
the action mode, refer to the section of “direct/reverse conversion of
positioner.”
If the input signal from the controller increases when the positioner is in
balanced state, the input lever moves in response to the air pressure
increment, nozzle #1 is closed and nozzle #2 is opened resulting in the
increased back-pressure for the nozzle #1 and the reduced back-pressure for
the nozzle #2. The variations of the back pressures are amplified with the
pilot relay and are fed to the actuator. The air pressure variation at the
actuator is converted into movement of the actuator stem (valve opening).
The movement of the stem back spring so that a negative feedback is effected
with respect to the torque variation caused by the input bellows and, thus,
the input lever is pushed back by the actuator stem to the position
corresponding to the input signal and the balanced state is attained.
When external disturbances are caused to the control valve and the actuator
stem is displaced, the resultant effect is the same with that the torque being
exercised on the input lever is varied and, therefore, the same automatic
balancing operation is performed.
SPECIFICATIONS
Input air pressure:……………… 0.2 to 1.0 kgf/cm? 0.2 to 0.6 kgf/cm 0.6 to 1.0
kgf/cm?
Supply air pressure:…………………. 1 2.0 to 3.5 kgf/cm? + 5%, 2 3.6 to 7.0 kgf/cm?
- 5%
Stroke adjustment range: ……………………………..14 to 100 mm
Cam characteristics
(No. 1): …………………………….Linear
(No. 2):…………………..Quick opening
(No. 3):………………….. Equal percentage
Ambient temperature limit: …………….-30 to +80°C
Air consumption: ……………………..20 N&/min (Ps = 5 kgf/cm?)
Net weight:………………………………… Approx. 3.5 kg
Air connection: ……………………..Rc 1/4 (PT 1/4 female)
Housing:……………………….. Aluminium alloy cast, dark beige, leathertone finish
Linearity:…………………………… Less than + 1% F.S.
Hysteresis:…………………….. Less than + 1% F.S.
Dead band: ………………………………Less than 0.2% F.S.
Repeatability: ………………………Less than 0.5% F.S.
Reproducibility:………………….. Better than 1% F.S.
Supply air pressure characteristics: ………………..+ 0.5% F.S./t 0.5 kgf/cm?
(Note)
1: ………………..For low bias pilot relay (engraved “L”)
2:……………………… For high bias pilot relay (engraved “H”)
INSTALLATION
A. General
When the VPP positioner is ordered together with a control valve, the
positioner is installed on the valve and adjusted at the factory before
shipment.
In other cases, the positioner must be installed following the in- structions
given below. The installation work consists of three procedures of (2)
installation of motion connector, (3) installation of positioner, and (4)
adjustment after installation. ,
B. Installation of Motion Connector
Install the motion connector on the pointer using the counter-sunk screw and
toothed lock-washer, loosen the fillister-head screw, adjust the slide rail to
the right angle with respect to the actuator stem, and tighten the counter-
sunk screw and fillister-head screw under this state.
C. Installation of Positioner
(a) Holes for two mounting-screws (M8 screw, 57-mm interval) are Grilled in
the mounting-base. Install the mounting-base by means of these holes and using
two hex-head screws.
(b) Install the positioner on the mounting-plate with two hex-head screws and
two lock-washers. Installation can be conveniently made by using a box wrench
for M8 hex-head screw.
D. Adjustment After Installation
After the motion connector and positioner and installed, make adjustment as
follows:
(a) Connect air to the actuator through the pressure regulator, and adjust the
pressure to the actuator so that the actuator stem is placed in the center of
the stroke. If the actuator has a manual operating mechanism, move the
actuator stem to the center of the stroke by means of the manual operating
mechanism.
(b) Adjust the gradient of the motion connector so that both slide rail and
positioner lever is positioned at the right angle with respect to the actuator
stem and, under this state, tighten securely the counter-sunk screw. When this
is done, the slide rail and positioner lever should be mutually parallel.
(c) Mount the travel pin on the positioner lever, and insert it in the slide
rail.
E. Air Connection
Four air connections ([ISO R7 1/4″(PT 1/4) female]) are provided on the side
of housing. Connections for these air connectors should be made as follows:
| Mark | Meaning | Connection |
|---|---|---|
| I | Instrument | Controller output |
| S | Supply | Supply air |
| O | Output | Air chamber of actuator |
ADJUSTMENT
When the positioner is ordered to be delivered being installed on the valve, it is shipped after being installed on the valve and adjusted. In other cases, adjust the positioner as described in the following:
- Check that, when the actuator stem is set at the center position of the stroke, the positioner lever and the slide rail are mutually parallel. If they have not been correctly installed, adjust them referring to Section 4 “INSTALLATION.”
- Select a cam of the required characteristics (refer to Section 6 “OPERATION”) and install the cam in the way that the curved cam surface which provides the required stroke is positioned in the side toward the cam follower. In this case, the arrowhead direction of the cam (the side toward the cam follower) should conform with the moving direction of the actuator stem when the pneumatic control signal is increased. For example, when both positioner and actuator are of the direct action type, the actuator stem will move downward the pneumatic control signal increases from 0.2 kgf/cm? to 1.0 kgf/cm. In the case of this example, install the cam in such way that the arrowhead side of the cam (the side toward the cam follower) is directed downward. See Figure 6.)
- Move the travel pin to the point for the required stroke referring to the figures (unit in mm) marked on the positioner lever and fix the travel pin at this point.
- Set the pneumatic control signal at the starting pressure of the actuator (typically, at 0.2 kgf/cm“) and adjust the spring adjuster so that the actuator stem starts moving with this pressure.
- Set the pneumatic control signal at the full-stroke pressure of the actuator (typically, at 1.0 kgf/cm?) and read the stroke. If the stroke is insufficient, move the travel pin rightward; if it is too large, move the pin leftward.
- Repeat the procedures of (4) and (5) so that the actuator stroke becomes within the allowable range for the full range of the pneumatic control signal.
Note: When the mechanism is balanced with the actuator stem set at an intermediate position, a normal indication is that the pressure of the actuator air chamber is ap- proximately one-half of the air supply pressure. When the actuator air chamber pressure is too small, adjust it by adjusting the gap between the nozzle and flapper which are located at lower left as viewed from the front. To adjust the gap, rotate the nozzle. As the gap is made larger, the pressure becomes smaller; as it is made smaller, the pressure becomes larger.
OPERATION
A. Cam Selection
The VPP positioner is shipped with the linear characteristic cam (1) unless
otherwise specified. Other available characteristics are as with cams (2) and
(3) as shown in Figs. 2 and 3. Application and selection of these cams are
explained below.
Figure 5. Cam Installation
(a) Cam Application
In general, a valve plug of which flow characteristics are Suitable for the
conditions of a process is employed. So, in order that the valve opening is
proportional to the control signal, cam (1) — linear characteristics — is most
commonly used.
With a butterfly valve — the characteristics of which are determined by the
valve construction —, flow characteristics most suitable for the conditions of
the process may not be obtained. In such a case, a special cam is employed to
improve the flow characteristics. For example, in case that a reverse- acting
actuator is installed on a valve which operates in the normally-closed mode.
While the flow characteristic of the valve are as shown in Fig. 8-A, flow
characteristic of equal percentage may be required by the conditions of the
process. In such a case, cam (3) will be selected from a group of curves of
normally closed valves. Through combination of the selected cam with the
valve, quasiequal-percent characteristic as shown in Fig. 8-C can be obtained.
For combination with a direct-acting actuator for the normally open mode, cam
(2) which is of the reverse characteristic of the above must be selected.
(b) Cam Selection
Cam selection must be made in the following procedure.
- Determine the flow characteristic of the control valve.
- Find whether the control valve is normally open or nor- mally closed.
- Referring to Fig. 7 select a cam which will provide the flow characteristic suitable for the process.
B. Direct/Reverse Switching of Positioner
For switching between direct action and reverse action of the positioner,
proceed as follows:
(a) Interchange the two pipes which connect the positioner with the actuator.
(Reverse the relationship between the positioner output connection and the
cylinder of actuator.)
(b) Change the mounting direction of the cam so that the arrow mark directs
the reverse direction. (Refer to Section (“ADJUSTMENT. “)
(c) Adjust the start point and strike. (Refer to “ADJUSTMENT.”)
C. Change of Positioner Range
Three feedback springs are available for individual control pressure ranges as
tabulated below. In the case of split range, a proper one must be selected
referring to the table.
Table of Feedback Springs
| Control pressure range | Color code |
|---|---|
| 0.2 to 1.0 kgf/cm2 | Green |
| 0.2 to 0.6 kgf/cm2 | Orange |
| 0.6 to 1.0 kgf/cm2 White | White |
When cam (1) — linear characteristics — is installed, range change can be made simply by adjusting the start point and stroke. For example, up to maximum 50 mm stroke, a standard spring of 0.2 to 1.0 kgf/cm? can be used as a split split spring of 0.2 to 0.6 kgf/cm2 or 0.6 to 1.0 kgf/cm? or other range.
MAINTENANCE
(a) As for the supply air, use clean and dry air.
(b) The parts* which have been moved for adjustment must be tightened securely
after the adjustment is over.
- Motion connector, counter-sink screw, fillister-head screw, travel pin, etc.
Each of the zero adjustment and nozzle is provided with a self-lock consisting of a leaf spring and a coil spring, and need not be tightened.
(c) When the gap between nozzle and flapper had been disturbed and the pressure under the balanced state of the actuator has become abnormal, move inward or outward the nozzle (located lower left as viewed from the front) so that the above pressure at no load becomes approximately a half of the supply air pressure. The pressure increases as the gap between nozzle and flapper is decreased, and vice versa.
(d) The pilot relay should not be disassembled by the customer.
When the pilot relay has become malfunctioning, the overall pilot relay should be replaced. The pilot relay can be removed after undoing the two clamping- screws.
Document Number: OM2-8310-0300
Document Name: Double Acting Pneumatic Valve Positioner
Model : VPP02/VPP03 User’s Manual
Date: 4th edition: Dec. 2013
Issued/Edited by: Azbil Corporation
References
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