Samson 4765 Service manual

Pneumatic Positioner
Type 4765
Fig. 1 · Type 4765 Positioner
Mounting and
Operating Instructions
EB 8359-1 EN
Edition April 2008

Contents
1 Design and principle of operation. . . . . . . . . . . . . . . . . . . . 6
2 Attachment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1 Attachment to valves with cast yokes . . . . . . . . . . . . . . . . . . . 8
2.2 Attachment to valves with rod-type yokes . . . . . . . . . . . . . . . . 9
2.3 Cover of the positioner housing . . . . . . . . . . . . . . . . . . . . . 9
3 Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1 Pneumatic connections. . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1.1 Pressure gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1.2 Supply pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4 Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1 Combining positioner and actuator. . . . . . . . . . . . . . . . . . . 11
4.1.1 Determining/reversing the operating direction . . . . . . . . . . . . . 11
4.2 Starting point and input signal (reference variable) . . . . . . . . . . . 12
4.3 Setting the positioner at the valve. . . . . . . . . . . . . . . . . . . . 14
4.3.1 Setting the air delivery (volume restriction Q) and proportional band XP . 14
4.3.2 Setting actuator version “Stem extends” . . . . . . . . . . . . . . . . 15
4.3.3 Setting actuator version “Stem retracts”. . . . . . . . . . . . . . . . . 15
4.4 Exchanging the range spring. . . . . . . . . . . . . . . . . . . . . . 16
5 Converting a pneumatic positioner. . . . . . . . . . . . . . . . . . . 17
6 Accessories, mounting parts and conversion kits . . . . . . . . . . . . 19
7 Dimensions in mm. . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2EB 8359-1 EN
Contents

EB 8359-1 EN 3
Safety instructions
General safety instructions
4
The positioner is to be mounted, started up or operated only by trained and
experienced personnel familiar with the product.
According to these Mounting and Operating Instructions, trained personnel
refers to individuals who are able to judge the work they are assigned to
and recognize possible dangers due to their specialized training, their
knowledge and experience as well as their knowledge of the applicable
standards.
4
Any hazards that could be caused by the process medium, the operating
pressure, the signal pressure or by moving parts of the control valve are to
be prevented by means of the appropriate measures.
4
If inadmissible motions or forces are produced in the pneumatic actuator as
a result of the supply pressure, the supply pressure must be restricted by a
suitable supply pressure reducing station.
4
Proper shipping and appropriate storage are assumed.

4EB 8359-1 EN
Versions
Pneumatic Positioner Type 4765- 01x00x 1 xxxx0
Range spring
Range spring 1, travel = 15 mm 1
Range spring 2, travel = 30 mm,
split-range 15 mm 2
Range spring 3, travel = 60 mm,
split-range 30 mm 3
Pneumatic connections
ISO 228/1 G ¼ 1
¼-18 NPT 3
Temperature range
Standard 0
Low temperature down to –50 °C 1
Special version
None 000
For oxygen as the operating medium 001

EB 8359-1 EN 5
Type 4765 Positioner
Travel range 7.5 to 60 mm, with 90 mm lever extension
Reference variable
Split-range 0 to 50 %
and 50 to 100 %
(up to 50 mm travel)
0.2 to 1 bar
0.2 to 0.6 bar and 0.6 to 1 bar
Range spring See table on page 13
Supply air 1.4 to 6 bar (20 to 90 psi)
Output signal pressure pst Max. 0 to 6 bar (0 to 90 psi)
Characteristic Linear · Deviation from terminal-based conformity: £1.5 %
Hysteresis < 0.5 %
Sensitivity < 0.1 %
Operating direction Reversible
Proportional band Xp
(at 1.4 bar supply air) 1 to 3 % with spring 1 or 2 1 to 1.5 % with spring 3
Air consumption in
steady state, Xp= 1 % With 1.4 bar supply air: 0.13
mn³/h With 6 bar supply air: 0.33 mn³/h
Air output capacity At Dp 1.4 bar: 3.0 mn³/h At Dp 6 bar: 8.5 mn³/h
Transit time for Type 3271 Actuator
“Stem extends” 240 cm²: £1.8 s · 350 cm²: £2.5 s · 700 cm²: £10 s
Permissible ambient temperature –20 to +80 °C · Extended temperature range on request
Influences Temperature < 0.02 %/1 K
Supply air < 0.2 %/0.1 bar
Effect when turned by 180°: < 3.5 %
Degree of protection IP 54 · Special version IP 65
Weight Approx. 1.1 kg
Materials Housing: Die-cast aluminum, chromated and plastic-coated
External parts: Stainless steel

1 Design and principle of
operation
The pneumatic positioner is used for the cor-
relation between the valve stem position
(controlled variable x) and the input signal
(reference variable w).
In this case, the input signal issued by a con-
troller is compared to the travel (valve stem
position) of the control valve, and a pneu-
matic signal pressure (output variable y) is
delivered.
The positioner consists of a lever with at-
tached shaft and range spring, diaphragm
and the pneumatic control system compris-
ing nozzle, flapper plate and booster.
In addition, a pressure gauge can optionally
be attached for the instrument input signal
and the positioner output signal.
The positioner operates according to the
force-balance principle. In this way, the
stroke of the actuator stem or the plug stem
(controlled variable x) is transmitted to the
lever (1) and the range spring (6) by the
plate (20). This action twists the range
spring and varies the torsional force.
The input signal (pe) supplied by the up-
stream controller produces a positioning
force on the diaphragm (8). This force is
compared with the force of the range spring
(6). At the same time, the motion (deflection)
of the diaphragm is transmitted to the flap-
per plate (10.2) by the feeler pin (9.1),
causing pressure to be released from the
nozzle (10.1).
Supply air is supplied to the pneumatic
booster (12) and flows through the Xpre-
striction (13) and the nozzle (10.1) until it
hits the flapper plate (10.2).
6EB 8359-1 EN
Design and principle of operation
10.21314
3
1
15
7
8
4 5 6.1 6
Fig. 2 · Positioner with cover removed

Any changes of the input signal peor the
valve stem position cause the pressure up-
stream and downstream of the booster to
change. The air released by the booster (sig-
nal pressure pst) flows to the pneumatic actu-
ator over the volume restriction (14), caus-
ing the plug stem to take on a position cor-
responding to the reference input variable.
The adjustable tuning restrictions (13 and
14) are used to optimize the control loop.
The range spring (6) corresponds to the
rated valve travel and the nominal reference
input span. It can be exchanged.
EB 8359-1 EN 7
Design and principle of operation
1.1 122.1 20
4
6
8
9
9.1
10.2
10
10.1
11
pst
Output 36
Supply 9 pe
Input
27
6
8
9
9.1
12.2
10.1
10
12
14
13
Fig. 3 · Functional diagram
Legend for Figs. 2 and 3
1 Lever for valve travel
1.1 Shaft
2 Pin
2.1 Nut
3 Sleeve
4 Zero adjustment screw
5 Mounting screw
6 Range spring
6.1 Bracket
7 Mounting screw
8 Measuring diaphragm
9 Diaphragm lever
9.1 Feeler pin
10 Nozzle block
10.1 Nozzle
10.2 Flapper
11 Cover plate
12 Booster
13 Xp restriction
14 Volume restriction Q
15 Hole for mounting screw
20 Plate
Arrangement of nozzle/flapper for
reverse operating direction <>
Travel

2 Attachment
To attach the positioner to valves with cast
yokes, mounting parts (order no.
1400-5745) are used. For valves with
rod-type yokes (pillars), the mounting kit (or-
der no. 1400-5745) and additionally the
mounting kit (order no. 1400-5342) are
necessary (see also Table 2 on page 19).
Since the positioner can be attached on ei-
ther side of the valve, the physical location
(left or right attachment) should be deter-
mined before actual attachment (see corre-
sponding Figs. 6 to 9 in section 4.1).
2.1 Attachment to valves with
cast yokes
1. Fasten the plate (20) to the stem connec-
tor clamps (22) of the valve using the
screws (21).
2. Unscrew the positioner cover, and secure
the device to the valve yoke using the
mounting screw (15). The O-ring in-
cluded in the mounting kit is not required
for this device. Make sure that the pin (2)
is routed inside the wire strap and there-
fore clamped against the plate (20).
8EB 8359-1 EN
Attachment
Legend for Figs. 4 and 5
1 Lever
2 Pin
2.1 Nut
15 Mounting screw
20 Plate
21 Screw
22 Stem connector
23 Plug stem
24 Travel indicator
26 Clamping plate
27 Valve rod (pillar)
28 Support
15 1 20 2 2.1 21 22 23
Fig. 4 · Attachment to valves with cast yokes (NAMUR rib)

2.2 Attachment to valves with
rod-type yokes
1. Screw the plate (20), off-centered, to the
travel indicator (24) of the plug stem (23)
using the screws (21).
2. Place both the support (28) and the
clamping plate (26) on the rod (27) and
lightly fasten. Move the support until both
the center of the plate (20) and the sup-
port (28) are aligned at half the valve
travel.
3. Screw tight the support and clamping
plate.
4. Mount the positioner to the support using
the mounting screw (15). Make sure that
the pin (2) is led inside the wire strap
and therefore clamped against the plate
(20).
2.3 Cover of the positioner
housing
After attaching the positioner, make sure
that the vent plug on the cover of the
positioner housing points downwards after
the valve has been installed.
EB 8359-1 EN 9
Attachment
151282726202.12 212423
Fig. 5 · Attachment to valves with rod-type yokes

3 Connections
3.1 Pneumatic connections
The pneumatic connections are designed as
tapped holes with ¼ NPT or ISO 2228/1-
G ¼ thread. The conventional male connec-
tions for metal and copper pipes (or plastic
hoses) can be used.
Note:
The supply air must be dry and free of any
oil and dust. Always observe the mainte-
nance instructions applicable to the con-
nected pressure reducing stations. Blow out
air lines thoroughly before connecting them.
3.1.1Pressure gauges
We recommend attaching pressure gauges
for the supply air and signal pressure in or-
der to monitor the positioner. The parts are
listed as accessories in Table 2 on page 19.
3.1.2Supply pressure
The required supply pressure is determined
by the bench range and the operating direc-
tion (fail-safe action) of the actuator.
The bench range is written on the nameplate
as spring range or signal pressure range
depending on the type of actuator. FA (actu-
ator stem extends) or FE (actuator stem re-
tracts) or a symbol indicates the operating
direction.
Actuator stem extends (FA)
Fail-safe position Valve CLOSED
(for globe and angle valves)
Required supply pressure =
Upper bench range value + 0.2 bar,
minimum 1.4 bar.
Actuator stem retracts (FE)
Fail-safe position Valve OPEN
(for globe and angle valves)
The required supply pressure for a
tight-closing valve is roughly estimated from
the maximum signal pressure pstmax:
pstmax = F + dp
A
2
4
××
×
pD [bar]
d = Seat diameter [cm]
Dp = Differential pressure across valve [bar]
A = Actuator diaphragm area [cm²]
F = Upper bench range of actuator [bar]
In the absence of such specifications, pro-
ceed as follows:
Required supply pressure =
Upper bench range value + 1 bar
The signal pressure (output) is routed to the
top or bottom diaphragm case of the actua-
tor as shown in Figs. 6 to 9.
10 EB 8359-1 EN
Connections