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Valve sizing and selection (steam) – Powers 596 SI Flowrite II Heavy Duty Control Valves User Manual

Page 4

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Page 4

Form TI 596SI v2

VALVE SIZING AND SELECTION (STEAM)

Steam:

One can use the same reasoning for selecting a valve in steam applications
as would be used for water applications. Once again, pressure drop
selection is a major determining factor for good control and system
performance. In general, for steam applications, the largest possible
pressure drop should be taken without exceeding the critical pressure ratio.

On/Off Control:
These types of applications are normally line sized to reduce pressure drop.
In these applications it is important to verify valve seat leakage will not
result in system overheat or damage. If this is a concern, it is necessary to
take precautions to alleviate this potential problem.

Proportional Control:

For pressures less than 15 psig, use an 80% of the gauge inlet pressure as a
differential. For pressures above 15psig, use 50% of the absolute inlet
pressure. In those cases where the required Cv falls between two valves,
select the larger size.

One may be concerned about steam entering a heating coil at 0 psig when
these large pressure drops are taken at the valve. However, flow will
continue as the pressure in the coil will drop to vacuum pressures due to
the steam condensation. It is essential to use proper condensate piping
and steam trapping in these applications.

Table - 3

Steam Capacity in Pounds Per Hour

Steam Inlet Pressure (psig)

2

5

10

Pressure Drop
Across Valve (psi)

0.5

1

2

1

2

3

4

5

2

4

6

8

10

Valve

Cv

Size

Rating

2.5

65

554

777

1082

846

1181

1426

1624

1790

1329

1839

2203

2484

2709

3

85

724

1016

1415

1106

1544

1865

2124

2341

1738

2405

2880

3249

3543

4

145

1235

1733

2413

1887

2634

3182

3623

3993

2965

4103

4914

5542

6044

5

235

2002

2809

3911

3058

4268

5157

5872

6472

4805

6650

7964

8981

9796

6

350

2981

4184

5825

4555

6357

7681

8746

9639

7156

9905

11861

13376

14589

Steam Inlet Pressure (psig)

15

25

50

Pressure Drop

(max)

(max)

(max)

Across Valve (psi)

3

6

9

12

15

5

10

15

20

10

20

30

32.5

Valve

Cv

Size

Rating

2.5

65

1776

2443

2907

3255

3523

2633

3596

4242

4705

4717

6385

7454

7660

3

85

2322

3195

3802

4257

4607

3443

4702

5548

6152

6168

8350

9747

10017

4

145

3961

5450

6485

7262

7858

5873

8022

9464

10495

10522

14243

16628

17088

5

235

6419

8834

10511

11770

12736

9518

13001

15338

17010

17053

23084

26949

27694

6

350

9561

13156

15654

17529

18968

14176

19363

22844

25334

25397

34380

40137

41247

Steam Inlet Pressure (psig)

75

100

125

Pressure Drop

(max)

(max)

(max)

Across Valve (psi)

10

25

35

45

10

25

36

58

20

50

70

Valve

Cv

Size

Rating

2.5

65

5618

8481

9704

10615

6394

9758

11390

13610

9832

14619

16526

3

85

7347

11090

12690

13882

8361

12760

14894

17797

12857

19117

21611

4

145

12533

18918

21647

23681

14263

21767

25408

30360

21932

32611

36866

5

235

20312

30661

35084

38379

23116

35277

41178

49205

35546

52853

59748

6

350

30251

45665

52252

57160

34428

52541

61329

73284

52940

78717

88987

Steam Inlet Pressure (psig)

150

175

200

Pressure Drop

(max)

(max)

(max)

Across Valve (psi)

25

50

83

50

70

95

50

75

108

Valve

Cv

Size

Rating

2.5

65

11908

16134

19521

17518

20088

22437

18800

22254

25431

3

85

15572

21098

25527

22908

26269

29340

24585

29102

33256

4

145

26563

35990

43546

39078

44812

50051

41939

49644

56731

5

235

43051

58329

70574

63334

72627

81117

67971

80457

91944

6

350

64118

86873 105111

94327

108167

120813

101233

119830

136937