**Control valves for steam and superheated steam**

## Calcultion of Cv and mass flow through the valve

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1. Cv
and Kv definition

2. Calculation of Cv and flow
through a valve - Case of liquids - SI units

3. Calculation of Cv and flow through a valve - Case of gases - SI
unitsb

4. Control valves sizing

5. Calculation of flow through a
valve - US units

**1. Cv and Kv definition**

### What is the flow coefficient Cv and Kv - calculation of flow
through a valve - SI units

**2. Calculation of Cv and flow through a valve - Case of steam -
SI units**

### What is the flow of steam through a valve ?

**The mass flow rate of steam** through a valve can be
calculated from the valve Cv thanks to the following formula :

With

m=Flow rate (t/h)

F_{L} = critical flow factor

C_{v}=valve flow coefficient (GPM)

P_{1} = upstream pressure (bar abs)

y = (1.63/F_{L})*√(ΔP/P_{1})

- If y < 1.5, subcritical flow
- if y > 1.5, then y is capped at y = y
_{max} =1.5 for
critical flow

**3. Calculation of Cv and flow through a valve - Case of
superheated steam - SI units**

### What is the flow of superheated steam through a valve ?

**The mass flow rate of superheated steam** through a valve can
be calculated from the valve Cv thanks to the following formula :

With

m=Flow rate (t/h)

F_{L} = critical flow factor

C_{v}=valve flow coefficient (GPM)

P_{1} = upstream pressure (bar abs)

T_{sh} = steam superheated temparature (c)

y = (1.63/F_{L})*√(ΔP/P_{1})

- If y < 1.5, subcritical flow
- if y > 1.5, then y is capped at y = y
_{max} =1.5 for
critical flow

**4. Control valve sizing**

### What are the best practices to size control valves ?

In order to have a good control, the design of the control valve
should be such that it represents around 1/3 of the total pressure
drop of the line. The valve must also be designed to work at flows
corresponding to 50 to 80 percent of the Cv of the valve.

**5. Steam and superheated valve sizing - US units**

**The sizing of a control valve for steam (2 first equations) and
superheated steam (2 last equations) can be calculated thanks to the
following equations in US units**

** **

With P1 in Psi, ΔP in Psi, m in lb/h, C_{v}in GPM, Tsh in F

**Source**

**Masoneilan Control Valve Sizing
Handbook, 2000**