Installed Gain as a Control Valve Sizing Criteria Jon Monsen, Ph.D., P.E.

transcript

Installed Gain as a Control Valve Sizing

Criteria

Jon Monsen, Ph.D., P.E.

Control Valve Characteristics

• Inherent• Installed

VALVE TRAVEL

What you need to remember about the inherent characteristic:

1. It is the relationship between valve opening

and flow capacity (CV) of

the valve while the pressure drop is held constant. (No system effects.)

2. It is the characteristic that is published by the manufacturer.

Inherent Characteristic

VALVE TRAVEL(PERCENT OF RATED TRAVEL)

50 1000 60 70

CV is linear with valve travel.

10 20 30

Linear

What you need to remember about the linear characteristic:

1. Its graph is a straight line.

2. It is only used about 10% of the time.

Equal changes in Valve Position produce equal percentage changes in flow capacity.

What you need to remember about the equal percentage characteristic:

1. The shape of the graph

2. It is used about 90% of the time.

VALVE TRAVEL(PERCENT OF RATED TRAVEL)

50 1000 60 70

80 9010 20 30

Equal Percentage (=%)

+10 = 50%

+22.5 = 50%

+15 = 50%

Installed Characteristic

0 10 20 30 40 50 60

Pressure

source

50 psig

280’ 1.5” pipe

050 0 gpm

0 10 20 30 40 50 60

FLOW (gpm) 10PIPE LOSS 1VALVE P 49

Pressure

source

50 psig

280’ 1.5” pipe049

10 gpm

CraneTechnical Paper 410

(1942) www.tp410.com

0 10 20 30 40 50 60

Pressure

source

50 psig

3.5 46.5

280’ 1.5” pipe

FLOW (gpm) 10 20PIPE LOSS 1 3.5VALVE P 49 46.5

46.5 020 gpm

0 10 20 30 40 50 60

Pressure

source

50 psig

7.5 42.5

42.5280’ 1.5” pipe

FLOW (gpm) 10 20 30PIPE LOSS 1 3.5 7.5VALVE P 49 46.5 42.5

030 gpm

0 10 20 30 40 50 60

Pressure

source

50 psig

37280’ 1.5” pipe

FLOW (gpm) 10 20 30 40PIPE LOSS 1 3.5 7.5 13VALVE P 49 46.5 42.5 37

040 gpm

0 10 20 30 40 50 60

Pressure

source

50 psig

30280’ 1.5” pipe

FLOW (gpm) 10 20 30 40 50PIPE LOSS 1 3.5 7.5 13 20VALVE P 49 46.5 42.5 37 30

050 gpm

0 10 20 30 40 50 60

Pressure

source

50 psig

22280’ 1.5” pipe

FLOW (gpm) 10 20 30 40 50 60PIPE LOSS 1 3.5 7.5 13 20 28VALVE P 49 46.5 42.5 37 30 22

060 gpm

0 10 20 30 40 50 60

Pressure

source

50 psig

22280’ 1.5” pipe

FLOW (gpm) 10 20 30 40 50 60PIPE LOSS 1 3.5 7.5 13 20 28VALVE P 49 46.5 42.5 37 30 22

060 gpm

Installed CharacteristicF

VALVE TRAVEL

Pressure

source

50 psig

Rule of Thumb:

Lots of pipe, use Equal Percentage valve

r inst

280’ 1.5” pipe

0 10 20 30 40 50 60

VALVE TRAVEL0

0 10 20 30 40 50 60

Pressure

source

50 psig

2.8’ 1.5” pipe

r inher

0.28 psi drop @ 60 gpm

Rule of Thumb:

Very little pipe, use Linear valve

Installed CharacteristicF

Valve Travel, h

Gain = Output / Input

Installed Characteristic and Gain

Gain = q / h

Valve Travel, h

Gain = q / h = SLOPE

Valve Travel, h

q = h X Gain

Valve Travel, h

q = h X Gain

Valve Travel, h

q = h X Gain

Valve Travel, h

Gain = d q / d h = SLOPE

Valve Travel, h

Within the specified control range:

1. Gain 0.5

2. Gain 3.0

3. Gain (max) / Gain (min) 2.0

Gain = q / h

q = h X Gain

Installed Gain Recommendations

ain 3.0

q min q maxFlow

1. Gain 0.5

2. Gain 3.0

Gain = q / h

q = h X Gain

Loop Tuned here

Data courtesy of ExperTune, Inc.

Large gain change:Can’t maintain good control with stability throughout flow range.The “un-tunable” loop!

ain 3.0

q min q maxFlow

ain 3.0

q min q max

1. Gain 0.5

2. Gain 3.0

Gain = q / h

q = h X Gain

Loop Tuned here

Data courtesy of ExperTune, Inc.

Small gain change:Good control with stability throughout flow range.

ain 3.0

q maxq min

1. Gain 0.5

2. Gain 3.0

4. As constant as possible

5. As close to 1.0 as possible

Gain = q / h

q = h X Gain

ain 3.0

q min q maxFlow

Valve Travel

Actual inherent flow characteristic Actual system characteristicFlow, gpm

P1 = 42

P1 = 32

P2 = 10 P2 = 12

P1 = 36

P2 = 11

MinNorm

0 100 200 300 400 500 600 700 800

Software Graphs Installed Characteristic & Gain

qf=766

6” Sch. 40

580’(Equiv. pipe & fittings)

230’

70F Water

10P2P1PP

=% Inherent characteristic

Flowgpm

psigPipeLoss(up)

psigPipeLoss

(down)

psig P

80 42 0.1 42 0.05 10 32

550 37 5.0 32 2.00 12 20

0 100 200 300 400 500 600 700 800

Flow, gpm

P1 = 42

P1 = 32

P2 = 10 P2 = 12

Sizing Example

Cv QGP

Sizing Example

85 dBA for 6”32.8 fpsp < pT

Sizing Example

80 dBA for 3”32.8 fps

Sizing Example

p < pT

6” 3”

Sizing Example

6” 3”

80 550

q maxq min

q min q max

1. Gain 0.5

2. Gain 3.0

Sizing Example

What is the optimum control valve pressure drop to design into a system to ensure adequate control while avoiding the use of excessive pumping power?

Selecting the Right Pump

Pump head droops 5 psi from 100 gpm to 600 gpm

Pressure losses @600 gpm

6” Sch 40

70°F Water

0 100 200 300 400 500 600

P1 (Pump A) 17 hp*35 2050

P1 (Pump B) 23 hp*6050

* At normal flow (400 gpm)

P1 (Pump C) 29 hp*7565

valve characteristic

Min. Norm. Max.

PRESSURE DROP = 5 psi @ MAX. FLOWPump power = 17 hp @ 400 gpm

Selecting the Right PumpPRESSURE DROP = 5 psi @ MAX. FLOW

Pump power = 17 hp @ 400 gpm

5 psi, 17 hp

20 psi, 23 hp

35 psi, 29 hp

q maxq min

q min q max

1. Gain 0.5

2. Gain 3.0

20 psi, 23 hp

35 psi, 29 hp

Maximum Calculated SPLTo avoid cavitation damage

UP TO 3” 80dBA4” TO 6” 85 dBA8” TO 14” 90 dBA16” AND UP 95 dBA

Thank you!

jmonsen@technical-controls.com

Installed Gain as a Control Valve Sizing Criteria Jon Monsen, Ph.D., P.E.

Documents