Question

An actuator has a stem movement which at full travel is 40 mm. It is mounted on a process control valve with an equal percentage plug and which has a minimum flow rate of 0.2 m3/s and a maximum flow rate of 4.0 m3/s. What will be the flow rate when the stem movement is (a) 10 mm, (b) 20 mm

Answer 1

Answer:

a) for a stem of 10 mm the flow rate is 0.4229 m³/s

b) for a stem of 20 mm the flow rate is 0.8944 m³/s

Explanation:

The mathematical expression for the flow rate is:

$Q=Q_{min} *(\frac{Q_{max} }{Q_{min} } )^{\frac{S-S_{min}}{S_{max}-S_{min} } }$

a) Here:

Qmin=0.2m³/s

Qmax=4m³/s

Smax-Smin=40mm

S-Smin=10mm

Substituting these values ​​in the first equation:

$Q=0.2*(\frac{4}{0.2} )^{\frac{10}{40} } =0.4229m^{3} /s$

b) In this time, S-Smin=20mm

$Q=0.2*(\frac{4}{0.2} )^{\frac{20}{40} } =0.8944m^{3} /s$