Control valves

Positioners and controllers

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Steam capacities in kg/h

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* Note:

The 37DE is limited to a

maximum pressure of 10 bar.

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Kv values

Size

Kvs

DN15LC

1.0

DN15

2.8

DN20

5.5

DN25

DN32

12.0

DN40

17.0

DN50

28.0

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The capacity varies for both the 37D and 37DE according to the pressure drop across them. The chart above enables the capacity to be

read off for different pressure drops. The maximum capacity occurs when the downstream pressure is at, or below 58% of the absolute

upstream pressure (Critical pressure drop). For many applications, valves can be satisfactorily sized on 10% pressure drop, i.e. with a

downstream which is 90% of the absolute upstream and a 10% pressure drop line is included in the chart to allow this to be done easily.

How to use the chart

The way in which the chart is used is explained by examples:

Example 1. Firstly, to find the size of control valve required to pass 200 kg/h with an upstream pressure of 8 bar and a permissable

pressure drop of 2 bar (downstream pressure = 6 bar)

Find the point at which the curved 8 bar upsteam pressure line intersects a horizontal line drawn from a downstream pressure of 6 bar and

read vertically downwards. It will be seen that a DN15 valve will pass 200 kg/h and is the correct size to choose.

Example 2. A DN50 valve is operating on an upstream pressure of 10 bar and has to pass 3 500 kg/h. It is required to know the downstream

pressure and hence the pressure drop across the valve.

The flowrate 3 500 kg/h is read off the horizontal line at the bottom of the chart giving the capacity of the DN50 valve using the vertical

guide line read upwards from the 3 500 kg/h figure until you strike the curved 10 bar upstream pressure line and from this point read

horizontally to the left to meet the downstream pressure scale. This is at the 7 bar reading and the pressure drop across the DN50 valve

when passing 3 500 kg/h of steam is 3 bar giving a downstream pressure of 7 bar.

Example 3. Finally, if a 10% pressure drop is satisfactory and a valve is required to pass 1 000 kg/h with an upstream pressure of 14 bar find

the point where the 14 bar curved upstream pressure line intersects the 10% pressure drop line. From this point read vertically

downwards and it will be seen that a DN32 valve is the correct size.

37D and 37DE Pilot Operated Temperature Control Valve with SG Iron Body

TI-P102-01 CH Issue 4

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