Regulating/control valve calculation

Rules for the selection of a regulating valve:

Regulating valve throughput kv/kvs

The regulating/control valve is the type of pipe fittings most commonly used to control flow and pressure.

Correct selection of the control valve is necessary for the normal operation of the piping system. The Kvs value expresses the amount of flow in a regulating valve at a fully-open valve position and a pressure differential of 1 bar. The Kvs value is a special case of the Kv value, which indicates the flow at a given valve position and a pressure differential of 1 bar.

The formulas for calculating the Kv valve are presented in table 1.

Table 1.

  • P1 — inlet pressure of valve, bar;
  • P2 — pressure at the exit of the valve, bar;
  • dP=Р1 – Р2 — valve pressure changes, bar;
  • t1 — inlet temperature, 0C;
  • Q — fluid flow, m3/hour;
  • Qn — flow for gas, m3/hour;
  • G — flow for water vapor, kg/hour;
  • ρ — density kg/m3

Kv value is multiplied by coefficient k1 (Recommended range for k1 1,2-1,3): Kvs=k1*Kv. We get the value Kvs - conditional valve throughput.

We select regulating valve with the closest possible large Kvs value from catalogs.

When choosing a valve, it is also recommended to calculate the nominal diameter of the valve.


Nominal diameter of the regulating valve

The diameter of the regulating valve is usually less than the diameter of the pipe.

Formula for calculating valve diameter:

  • d — design valve diameter, mm;
  • Q — flow, m3/hour;
  • V – recommended flow rate m/s.

Recommended flow rate :

  • liquid – 3 m/s;
  • water vapor – 40 м/с;
  • gas (when pressure < 0,01 bar) – 2 m/s;
  • gas (0,01 – 0,1 bar) – 4 m/s;
  • gas (0,1 – 1,0 bar) – 10 m/s;
  • gas (1,0 – 10,0 bar) – 20 m/s;
  • gas ( > 10,0 bar) – 40 m/s;

We calculate the diameter (d) and select the closest larger nominal diameter (DN) of the valve.


Instruction:

1) Select type of transported substance (liquid / gas / water vapor).

2) Enter inlet pressure (Р1) and pressure at the exit of the valve (Р2).

!Attention! Pressure indicate in bar.

3) Enter flow m3/hour and substance density, kg/m3 (For gas and steam, indicate density for normal conditions).

4) Enter coefficient for converting kv to kvs (Recommended range 1,2-1,3).

5) For calculation, click the button "Calculation".

!Attention! Before a new calculation, click the "Reset" button.

Initial data:


Coefficients for regulating valve:

Kv=
Kvs=

Recommended nominal diameter (DN) of valve and flow rate (V):

Recommended flow rate (V) no more: m/s
Design valve diameter, mm: mm
Recommended nominal diameter DN, mm: mm