CONTROL VALVE HANDBOOK Episode 1 Part 7 potx

Chapter 5. Control Valve Selection

107

Fluid Compatibility (continued)

This table rates and compares the compatibility of elastomer material with specific fluids. Note that this information should be used as a guide only. An

elastomer which is compatible with a fluid may not be suitable over the entire range of its temperature capability. In general, chemical compatibility decreases

with an increase in service temperature.

KEY: A+=Best Possible Selection A=Generally Compatible B=Marginally Compatible C=Not Recommended −=no data

NOTE: These recommendations are to be used as a general guide only. Full details regarding pressure, temperature, chemical considerations, and the mode of

operation must be considered when selecting an elastomer.

FLUID

ELASTOMER RATINGS FOR COMPATIBILITY WITH FLUID

TFE/P

Tetra−

fluoro

ethylene−

propylene

copolymer

NR

Natural

Rubber

NBR

Nitrile

Buna N

VMQ

Silicone

IIR

Butyl

FFKM

Perfluoro−

elastomer

FKM

Fluoro−

elastomer

Viton(1)

EPM,

EPDM

Ethylene

Propylene

CR

Chloro−

prene

Neoprene(1)

CO, ECO

Epichloro

−hydrin

AU, EU

Poly−

urethane

ACM,

ANM

Poly−

acrylic

Steam

Sulfer Dioxide (Dry)

Sulfur Dioxide (Wet)

Sulfuric Acid (to 50%)

C

C

C

B

C

−

B

C

C

−

−

B

C

C

B

C

B+

A+

A+

B

C

−

C

A+

A

−

A

A

B

B

A

C

C

B

B

C

C

C

C

C

C

B

C

C

A+

−

B

A

Sulfuric Acid (50−100%)

Suva HCFC−123(1)

Suva HFC134a(1)

C

−

−

C

C

−

C

−

−

C

A+

B

C

A+

A

A+

B

C

A

−

−

C

A+

B

C

B

B

C

C

A+

C

C

B

A

−

Water (Ambient)

Water (200
F, 93
C)

C

C

C

C

B

B

A

C

A

A+

A

B

A

A

A

B

A

A

A

C

A

A

A

−

Water (300
F, 149
C)

Water (De−ionized)

Water, White

C

C

C

C

A

B

−

−

−

C

A

B

B+

A

A

C

A

A

A

A

A

B

A

A

C

A

B

C

A

B

C

A

B

−

A

−

1. Registered trademark of DuPont Performance Elastomers.

2. Trademark of Dow Chemical Co.

Chapter 5. Control Valve Selection

108

Service Temperature Limits for Non−Metallic Materials

ASTM Designations and

Tradenames Generic Description Temperature Range

CR Chloroprene −40 to 180
F, −40 to 82
C

EPDM Ethylene propylene terpolymer −40 to 275
F, −40 to 135
C

FFKM, Kalrez(1),

Chemraz(2) Perfluoroelastomer 0 to 500
F, −18 to 260
C

FKM, Viton(1) Fluoroelastomer 0 to 400
F, −18 to 204
C

FVMQ Fluorosilicone −100 to 300
F, −73 to 149
C

NBR Nitrile −65 to 180
F, −54 to 82
C

NR Natural rubber −20 to 200
F, −29 to 93
C

PUR Polyurethane −20 to 200
F, −29 to 93
C

VMQ Silicone −80 to 450
F, −62 to 232
C

PEEK Polyetheretherketone −100 to 480
F, −73 to 250
C

PTFE Polytetrafluoroethylene −100 to 400
F, −73 to 204
C

PTFE, Carbon Filled Polytetrafluoroethylene,

Carbon Filled −100 to 450
F, −73 to 232
C

PTFE, Glass Filled Polytetrafluoroethylene,

Carbon Filled −100 to 450
F, −73 to 232
C

TCM Plus(3) Mineral and MoS2 filled PTFE −100 to 450
F, −73 to 232
C

TCM Ultra(3) PEEK and MoS2 filled PTFE −100 to 500
F, −73 to 260
C

Composition Gasket −60 to 300
F, −51 to 150
C

Flexible Graphite, Grafoil(4) −300 to 1000
F, −185 to 540
C

1. Registered trademark of DuPont Performance Elastomers.

2. Trademark of Greene, Tweed & Co.

3. Trademark of Fisher Controls International LLC

4. Trademark of Union Carbide

Control Valve Flow

Characteristics

The flow characteristic of a control

valve is the relationship between the

flow rate through the valve and the

valve travel as the travel is varied

from 0 to 100%. Inherent flow charac￾teristic refers to the characteristic ob￾served with a constant pressure drop

across the valve. Installed flow char￾acteristic means the one obtained in

service where the pressure drop var￾ies with flow and other changes in the

system.

Characterizing control valves provides

for a relatively uniform control loop

stability over the expected range of

system operating conditions. To es￾tablish the flow characteristic needed

to match a given system requires a

dynamic analysis of the control loop.

Analyses of the more common pro￾cesses have been performed, howev￾er, so some useful guidelines for the

selection of the proper flow character￾istic can be established. Those guide￾lines will be discussed after a brief

look at the flow characteristics in use

today.

Flow Characteristics

Figure 5-1 illustrates typical flow char￾acteristic curves. The quick−opening

flow characteristic provides for maxi￾mum change in flow rate at low valve

travels with a nearly linear relation￾ship. Additional increases in valve

travel give sharply reduced changes

in flow rate, and when the valve plug

nears the wide open position, the

change in flow rate approaches zero.

In a control valve, the quick opening

valve plug is used primarily for on-off

service; but it is also suitable for many

applications where a linear valve plug

would normally be specified.