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

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.

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.

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.

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

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

9.1

10.2

10.1

pst

Output 36

Supply 9 pe

Input

9.1

12.2

10.1

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

××

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

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