Emerson Fisher 785C User manual

www.Fisher.com

Fisher™785C Piston Actuators

Contents

Introduction 1.................................

Scope of Manual 1.............................

Description 3.................................

Specifications 3...............................

Educational Services 3.........................

Principle of Operation 3.........................

Installation 7..................................

Actuator Earth Grounding 9.....................

Three‐Way Valve Applications Note 9.............

Manual Override 9.............................

Handwheel Operation 10.......................

Manual Hydraulic Handpump Operation 12........

Actuator Mounting 22...........................

Maintenance 23................................

Actuator Removal 23..........................

Disassembling the Pneumatic Cylinder 24.........

Replacing the Pneumatic Cylinder Seals 25........

Assembling the Pneumatic Cylinder 27...........

Lubrication 28................................

Disassembling the Handpump Hydraulic Cylinder 30

Handpump Hydraulic Cylinder Seals Replacement 30

Handpump Hydraulic Cylinder Reassembly 30.....

Other Maintenance Specifications 32.............

Troubleshooting 35.............................

Parts Ordering 36...............................

Parts Kits 36...................................

Parts List 47...................................

Assembly Drawings 50..........................

Figure 1. Fisher 785C Single-Acting Spring Return

with Handpump

X1851

Introduction

Scope of Manual

This instruction manual includes installation, maintenance, and parts information for the Fisher 785C piston actuator.

Refer to separate instruction manuals for information regarding other equipment and accessories used with these

actuators.

Do not install, operate, or maintain 785C actuators without being fully trained and qualified in valve,

actuator, and accessory installation, operation, and maintenance. To avoid personal injury or property

damage, it is important to carefully read, understand, and follow all the contents of this manual,

including all safety cautions and warnings. If you have any questions about these instructions, contact

your Emerson sales office before proceeding.

Instruction Manual

D104483X012

785C Actuator

May 2022

Instruction Manual

D104483X012

785C Actuator

May 2022

Table 1. Specifications

Operating Pressure(1)

Minimum: 2.7 barg (40 psig)

Maximum Allowable: 10.3 barg (150 psig)

Consult your Emerson sales office for supply

pressures under 2.7 barg (40 psig)

Travel(2)

16 mm (0.625 inch) through 610 mm (24 inch)

See table 2 and 4

Thrust Capabilities

See table 3, 6, and 7

Stroking Speeds

Varies with actuator size, spring, travel, and supply

pressure. If stroking speed is critical, consult your

Emerson sales office.

Piston Diameter and Area(2)

Available diameters range from 280 to 685 mm

(11 to 27 inches).

See table 2, 4, and 5

For additional sizes, contact your Emerson sales

office.

Operative Temperature Limits(3)

Standard: -20 to 100_C (-4 to 212_F)

Low Temperature Options:

-40 to 100_C (-40 to 212_F) or

-60 to 100_C (-76 to 212_F)

High Temperature Option:

-20 to 200_C (-4 to 392_F)

Yoke Boss and Valve Stem Diameter

Standard: J90 mm (3-9/16 inch) yoke boss with

19 mm (3/4 inch) stem J127 mm (5 inch) yoke boss

with 25.4 mm (1 inch) stem J127 mm (5H) yoke

boss with 32 mm (1-1/4 inch) stem J178 mm

(7 inch) yoke boss with 51 mm (2 inch) stem

High Performance: J127 mm (5H) yoke boss with

32 mm (1-1/4 inch) stem J178 mm (7 inch) yoke

boss with 51 mm (2 inch) stem

Pressure Connections

Standard: 3/4 NPT

Optional: 1 and 1-1/4 NPT

Instrument Mounting

Standard mounting kits are available for use with

FIELDVUE DVC6200 Series digital valve controllers up

to 610 mm (24 inch) travel. High performance

mounting kits are available for travel above 203 mm

(8 inch).

Construction Materials(4)

Part Material

Cylinder Carbon Steel

Nameplate and Travel Scale Stainless Steel

Piston Carbon Steel

Piston Rod Stainless Steel

Stem Connector Carbon Steel or Stainless Steel

Tie Rod Carbon Steel or Stainless Steel

Upper/Lower Heads Carbon Steel

Yoke Carbon Steel

Lifting Point Load Ratings

See table 8 and figure 2

Options

JTop mounted handwheel

JSide mounted handpump

JPneumatic fail mode via Fisher 377 trip valve

JVolume boosters

Optional Certifications(5)

JPressure Equipment Directive (PED) 2014/68/EU

and Machinery Directive 2006/42/EC

JATEX Group II Category 2 Gas and Dust

JCustoms Union Technical Regulations (CUTR)

010/2011 and 012/2011

JSafety Instrumented System, SIL 3 Capable

JInspection Documents EN 10204 3.1 Certificate

1. The pressure/temperature limits in this bulletin and any other applicable standard or code should not be exceeded.

2. Consult your Emerson sales office for longer travels or larger cylinder diameters. The Fisher 585C family of actuators can be used for smaller travels or cylinder diameters.

3 Standard temperature -20 to 100_C (-4 to 212_F) and -40 to 100_C (-40 to 212_F) are PED 2014/68/EU and 2006/42/EC compliant. The low ambient temperature option, -60 to 100_C (-76 to 212_F)

is not PED compliant. The high temperature option, if used in conjunction with ATEX, is limited to 135_C (275_F).

4. Full stainless steel constructions are available upon request.

5. Refer to the product nameplates to determine which certifications each actuator construction possesses

Instruction Manual

D104483X012

785C Actuator

May 2022

Description

The 785C product lines encompass medium to large spring-return single-acting and double-acting piston actuators

that provide accurate, high thrust output for short to long travel applications. These actuators are designed for use

with a variety of medium to large Fisher sliding-stem control valves.

The single-acting actuators feature an internal bias spring that forces the actuator piston rod to extend or retract upon

a loss of supply pressure, thereby ensuring a fail-closed or fail-open mode of operation. This effectively eliminates the

need for a trip valve and volume tank in most constructions.

Specifications

Specifications for the 785C line of piston actuators are shown in tables 1 to 8. Refer to the nameplate affixed to the

actuator yoke for specifications specific to individual constructions.

Educational Services

Emerson Automation Solutions

Educational Services - Registration

Phone: 1-800-338-8158

E-mail: [email protected]

emerson.com/mytraining

Principle of Operation

785C piston actuators utilize a pneumatically controlled piston that moves inside of a cylinder to generate thrust. A

seal contained on the circumference of the piston provides a seal between the top and bottom of the cylinder,

preventing supply pressure leakage.

785C single-acting or double-acting spring-return piston actuators utilize a spring below the piston (outside the

pressurized chamber) that will drive the piston rod upon a loss of supply pressure. This fail action will result in forcing

an attached control valve to either fail-open or fail-closed. The fail action of 785C double-acting springless piston

actuators relies on pneumatic system such as system with Fisher 377 trip valve.

From an equilibrium state, the actuator operates by reacting to a force unbalance that is created by change of supply

pressure on one side of the piston for single-acting, or a change of differential pressure between each side of the

piston for double-acting. This moves the piston up or down, and results in a repositioning of the attached control

valve. Travel can be adjusted using travel limits within a valve positioner, which limit the travel range of the actuator.

The option of a hard travel stopper is also available, consult your Emerson sales office for details. The optional manual

override does not have the ability to act as a hard travel stop.

An optional manual override (top mounted handwheel or side mounted handpump) is capable of extending or

retracting the actuator manually and can be engaged at any position from full open to full close. The top-mounted

handwheel utilizes an engagement lever that couples the handwheel and piston rod. The handpump has a hydraulic

cylinder attached to the piston rod. This enables the handpump to operate the actuator manually, unless the

handpump is set to bypass position.

Instruction Manual

D104483X012

785C Actuator

May 2022

Table 2. 785C Double-Acting Springless Standard Constructions(1)

ACTUATOR

SIZE

PISTON AREA VALVE STEM

CONNECTOR SIZE

YOKE BOSS

DIAMETER MAX TRAVEL

Without Manual

Override

With Manual

Override(2)

cm2Inch2cm2Inch2mm Inch mm Inch mm Inch

280 616 95 616 95

19 3/4 90 3 9/16 203 8

25 1 127 5

32 1 1/4 127 5H 610 24

335 881 137 881 137

19 3/4 90 3 9/16 203 8

25 1 127 5

32 1 1/4 127 5H 610 24

385 1164 180 1164 180

19 3/4 90 3 9/16 203 8

25 1 127 5

32 1 1/4 127 5H 610 24

51 2 178 7

435 1486 230 1474 228

25 1 127 5 203 8

32 1 1/4 127 5H 610 24

51 2 178 7

485 1847 286 1828 283

25 1 127 5 203 8

32 1 1/4 127 5H 610 24

51 2 178 7

535 2248 348 2228 345

25 1 127 5 203 8

32 1 1/4 127 5H 610 24

51 2 178 7

585 2688 417 2660 412 32 1 1/4 127 5H 610 24

51 2 178 7

635 3167 491 3139 487 32 1 1/4 127 5H 610 24

51 2 178 7

685 3685 571 3657 567 32 1 1/4 127 5H 610 24

51 2 178 7

1. Consult your Emerson sales office for additional sizes.

2. Actuator size 280-385 are available with a top mounted handwheel. Size 435-685 are available with a side mounted manual handpump.

3. High Performance Yoke required for ODV packages with travel greater than 8 inches. Optional for use in high vibration or fast stroke package. When ordering a high performance yoke boss

you will need to order a high performance mounting kit as well.

Table 3. 785C Double-Acting Springless Available Thrust

ACTUATOR SIZE

MAXIMUM ALLOWABLE

CYLINDER PRESSURE

MAXIMUM ALLOWABLE THRUST

Without Manual Override With Manual Override(1)

barg psig N lb N lb

280

10.3 150

63682 14316 32635 7337

335 91157 20493 46715 10502

385 120399 27067 61700 13871

435 153702 34554 78726 17698

485 191066 42953 132291 29740

535 232492 52266 132291 29740

585 277979 62492 172788 38844

635 327527 73631 172788 38844

685 381137 85683 238555 53629

1. Actuator size 280-385 are available with a top mounted handwheel. Size 435-685 are available with a manual handpump.

Instruction Manual

D104483X012

785C Actuator

May 2022

Table 4. 785C Single-Acting Spring Return Standard Constructions(1)

ACTUATOR

SIZE

PISTON AREA VALVE STEM

CONNECTOR

SIZE

YOKE BOSS

DIAMETER MAX TRAVEL

Without Manual Override With Manual Override(2)

Rod Extends Rod Retracts Rod Extends Rod Retracts

cm2Inch2cm2Inch2cm2Inch2cm2Inch2mm Inch mm Inch mm Inch

335 881.4 136.6 868.9 134.7 881.4 136.6 868.9 134.7

19 3/4 90 3 9/16

203 8

25 1 127 5

32 1 1/4 127 5H

385 1164 180.4 1152 178.5 1164 180.4 1152 178.5

19 3/4 90 3 9/16 203 8

25 1 127 5

32 1 1/4 127 5H 318 12

51 2 178 7

435 1486 230.4 1474 228.4 1474 228.4 1474 228.4

25 1 127 5 203 8

32 1 1/4 127 5H 420 16

51 2 178 7

485 1847 286.4 1835 284.4 1828 283.3 1835 284.4

25 1 127 5 203 8

32 1 1/4 127 5H 420 16

51 2 178 7

535 2248 348.4 2235 346.5 2228 345.4 2235 346.5

25 1 127 5 203 8

32 1 1/4 127 5H 420 16

51 2 178 7

585 2688 416.6 2660 412.2 2660 412.2 2660 412.2 32 1 1/4 127 5H 420 16

51 2 178 7

635 3167 490.9 3139 486.5 3139 486.5 3139 486.5 32 1 1/4 127 5H 420 16

51 2 178 7

685 3685 571.2 3657 566.8 3657 566.8 3657 566.8 32 1 1/4 127 5H 420 16

51 2 178 7

1. Consult your Emerson sales office for additional sizes.

2. Actuator size 335-385 are available with a top mounted handwheel. Size 435-685 are available with a side mounted manual handpump.

Table 5. 785C Double-Acting Spring Return Standard Constructions(1)

ACTUATOR

SIZE

PISTON AREA VALVE STEM

CONNECTOR

SIZE

YOKE BOSS

DIAMETER MAX TRAVEL

Without Manual Override With Manual Override(2)

Rod Extends Rod Retracts Rod Extends Rod Retracts

cm2Inch2cm2Inch2cm2Inch2cm2Inch2mm Inch mm Inch mm Inch

280 615.8 95.4 603.2 93.5 615.8 95.4 603.2 93.5

19 3/4 90 3 9/16

203 8

25 1 127 5

32 1 1/4 127 5H

335 881.4 136.6 868.9 134.7 881.4 136.6 868.9 134.7

19 3/4 90 3 9/16

203 8

25 1 127 5

32 1 1/4 127 5H

385 1164 180.4 1152 178.5 1164 180.4 1152 178.5

19 3/4 90 3 9/16 203 8

25 1 127 5

32 1 1/4 127 5H 318 12

51 2 178 7

435 1486 230.4 1474 228.4 1474 228 1473 228.4

25 1 127 5 203 8

32 1 1/4 127 5H 420 16

51 2 178 7

485 1847 286.4 1835 284.4 1828 283 1835 284.4

25 1 127 5 203 8

32 1 1/4 127 5H 420 16

51 2 178 7

535 2248 348.4 2235 346.5 2228 345 2235 346.5

25 1 127 5 203 8

32 1 1/4 127 5H 420 16

51 2 178 7

585 2688 416.6 2660 412.2 2660 412 2660 412.2 32 1 1/4 127 5H 420 16

51 2 178 7

635 3167 490.9 3139 486.5 3139 486.5 3139 486.5 32 1 1/4 127 5H 420 16

51 2 178 7

- continued -

Instruction Manual

D104483X012

785C Actuator

May 2022

Table 5. 785C Double-Acting Spring Return Standard Constructions(1) (continued)

ACTUATOR

SIZE

PISTON AREA VALVE STEM

CONNECTOR

SIZE

YOKE BOSS

DIAMETER MAX TRAVEL

Without Manual Override With Manual Override(2)

Rod Extends Rod Retracts Rod Extends Rod Retracts

cm2Inch2cm2Inch2cm2Inch2cm2Inch2mm Inch mm Inch mm Inch

685 3685 571.2 3657 566.8 3657 566.8 3657 566.8 32 1 1/4 127 5H 420 16

51 2 178 7

1. Consult your Emerson sales office for additional sizes.

2. Actuator size 280-385 are available with a top mounted handwheel. Size 435-685 are available with a manual handpump.

Table 6. Handwheel Specification

ACTUATOR

SIZE

OUTPUT THRUST HANDWHEEL DIAMETER TURNS PER mm

OF TRAVEL

TURNS PER INCH

OF TRAVEL

MAXIMUM RIM

FORCE REQUIRED

N lbs mm Inch N lbs

280 32635 7337 850 33 0.2 4.2 437 98

335 46715 10502 1200 47 0.2 4.2 435 98

385 61700 13871 1400 55 0.2 4.2 489 110

Table 7. Handpump Specification

ACTUATOR SIZE HYDRAULIC CYLINDER OUTPUT THRUST

mm Inch N lbf

435 135 5.3 78726 17698

485 175 6.9 132291 29740

535 175 6.9 132291 29740

585 200 7.9 172788 38844

635 200 7.9 172788 38844

685 235 9.3 238555 53629

Table 8. Lifting Point Load Ratings

ACTUATOR SIZE LIFTING ORIENTATION NUMBER OF LIFTING

POINTS USED

MAXIMUM WELDED EYELET LOAD

AT LIFTING ANGLE a3205

(SEE FIGURE 2)

Kg lbs

280

Actuator Centerline Horizontal(1)

2 1572 3466

335 2 1572 3466

385 2 1572 3466

435 2 1572 3466

485 2 5697 12560

535 2 5697 12560

585 2 5697 12560

635 2 5697 12560

685 2 5697 12560

ACTUATOR SIZE LIFTING ORIENTATION NUMBER OF LIFTING

POINTS USED

MAXIMUM LOAD AT EYEBOLT

LIFTING ANGLE a3455

(SEE FIGURE 2)

Kg lbs

280

Actuator Centerline Vertical(2)

4 864 1905

335 4 864 1905

385 4 864 1905

435 4 864 1905

485 4 3096 6826

535 4 3096 6826

585 4 3096 6826

635 4 3096 6826

685 4 3096 6826

1. Welded eyelets for horizontal lifting are only available for the 785C Spring Return.

2. Vertical lifting loads are applicable to both the 785C Springless and Spring Return.

Instruction Manual

D104483X012

785C Actuator

May 2022

Figure 2. Lifting Angle N

SPRING RETURN ACTUATOR

CENTERLINE HORIZONTAL LIFT

785C ACTUATOR

VERTICAL HORIZONTAL LIFT

Installation

Key numbers in this procedure are shown in figures 9 to 28, unless otherwise indicated.

WARNING

To avoid personal injury or property damage caused by cylinder fracture as a result of piston impact, install the stem

connector securely before supplying pressure to the positioner. Use only a regulator-controlled air supply to move the

actuator piston so that you can install the stem connector. Do not use the positioner to move the actuator piston before

installing the stem connector.

Always wear protective gloves, clothing, and eyewear when performing any installation operations to avoid personal

injury.

If installing into an existing application, also refer to the warning at the beginning of the Maintenance section in this

manual.

Check with your process or safety engineer for any additional measures that must be taken to protect against process

media.

To avoid personal injury or property damage caused by bursting of pressure‐retaining parts, be certain the cylinder

pressure or other pressure ratings do not exceed the limits listed in table 1. Use pressure‐limiting or pressure‐relieving

devices to prevent cylinder pressure or other pressures from exceeding these limits.

To avoid personal injury or equipment damage, use proper lifting and rigging practices while lifting the actuator or

valve/actuator assembly. For all mounting procedures use an adequately sized chain, sling, hoist, or crane to handle the

Instruction Manual

D104483X012

785C Actuator

May 2022

actuator and any attached accessories and/or valve. Use caution during lifting and handling to prevent slippage, swinging,

faulty equipment connections, or sudden shock loads.

NOTICE

Special care must be taken when installing an actuator in a horizontal service orientation. To avoid cantilever loads on the

valve stem and yoke, it is the customer’s responsibility to ensure proper support for a horizontal actuator.

The actuator may be installed in any orientation, but normal installation is with the actuator vertical above the valve.

If using a manual override in double acting application, a bypass valve should be furnished, allowing balance the

pressure within both sides of the piston before operating the manual override.

If using a manual handpump, the handpump must be installed vertical above the valve (see figure 7).

If the supply source is capable of exceeding the maximum actuator operating pressure or instrument supply pressure,

appropriate steps must be taken during installation to protect the instrument and all connected equipment against

overpressure.

When an actuator and control valve are shipped together as a control valve assembly, the actuator is normally

mounted on the valve. Follow the valve instructions when installing the valve in the pipeline. If the actuator is shipped

separately or if it is necessary to mount the actuator on the valve, perform the actuator mounting procedures in this

instruction manual. Refer to the individual product instruction manuals for the installation or mounting of a FIELDVUE

DVC6200 digital valve controller.

If the actuator is being installed without a positioner, the cylinder loading pressures should be supplied through a

4-way solenoid valve or a switching valve.

Pressure connections are located on top of the pneumatic cylinder end flange (key 2210) and on the side of the

pneumatic cylinder head flange (key 2201).

D The supply pressure medium should be clean, dry filtered air. If the supply source is capable of exceeding the

maximum actuator operating pressure or positioner supply pressure, appropriate steps must be taken during

installation to protect the positioner and all connected equipment against over pressurization.

D The control valve should be located where it will be accessible for servicing. Space should be left above and below

the control valve to permit removal of the actuator and valve plug.

Actuator Earth Grounding

All Fisher 785C series actuators are provided with a threaded actuator earth grounding interface on the yoke (spool)

for the earth connection as shown in the figure 3.

Note

Proper connection to the earth grounding interface is required for compliance with ATEX regulations.

Instruction Manual

D104483X012

785C Actuator

May 2022

Figure 3. Actuator Earth Grounding Interface

ACTUATOR EARTH

GROUND INTERFACE

Three‐Way Valve Applications Note

In three-way valve applications where the actuator fully strokes at a frequency of once per minute or faster, and the

stroking speed is rapid (less than 0.5 seconds per stroke), there is a possibility that the stem can fracture at the plug if

the actuator cylinder pressure is greater than 5.5 bar (80 psig). This can cause loss of control of process fluid and

further damage to the actuator. Considerations should be given to the use of high-strength, fatigue-resistant stem

materials in these applications.

WARNING

To avoid loss of control of process fluid and subsequent personal injury or property damage caused by bursting of

pressure‐retaining parts, be sure the cylinder pressure does not exceed 5.5 bar (80 psig) in high cycle‐rate, fast stroking

speed, three‐way valve applications.

Manual Override

The actuator can be equipped with a manual override. The manual override can be executed with a Manual Handwheel

or a Manual Hydraulic Pump which can operate the actuator.

Instruction Manual

D104483X012

785C Actuator

May 2022

Manual Handwheel Operation

If manual operation is required for actuator sizes 280, 335, and 385 a manual handwheel should be equipped as

standard construction.

NOTICE

To avoid damage to actuator parts and difficult operation of actuator handwheels, open the bypass valve before using a

handwheel. Do not disengage the handwheel if the spring thrust is not balanced by pneumatic load for spring return

actuator.

A bypass assembly is furnished only when an actuator with manual override is specified, see figure 4. The bypass

assembly allows the pressure to equalize on either side of the actuator piston, so that the manual override can be used

to position the control valve. Flow through the bypass tubing is controlled by an angle needle valve, which is operated

manually. This valve should be closed when air pressure is being used to operate the actuator.

Figure 4. Bypass Valve Examples for Double-Acting 785C Actuator with Manual Override

GH14579, sheet 1

ACTUATOR,

SPRING RETURN

GH14579, sheet 3

ACTUATOR,

SPRINGLESS

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