How do you design a control valve?

How do you design a control valve?

Valve Design Equation

1. The valve design equation relates the pressure drop ΔPv Δ P v across the valve to the volumetric flow rate q .
2. The Cv is a measure of the size of a valve and valve suppliers have different valve body sizes, each with a different Cv value.

How do you choose a control valve?

Valve characteristics selection guidelines

1. Type of fluid to be controlled.
2. Temperature range of fluid.
3. Viscosity range of fluid.
4. Specific gravity range of fluid.
5. Minimum and maximum flow required.
6. Minimum and maximum inlet pressure at the control valve.
7. Minimum and maximum outlet pressure at the control valve.

What is the CV rating on a control valve?

Valve Flow Coefficient (Cv) is the flow capability of a control valve at fully open conditions relative to the pressure drop across the valve. It is defined as the volume of water (GPM in the US) at 60°F that will flow through a fully open valve with a pressure differential of 1 psi across the valve.

What is valve trim size?

Valve trim is the physical shape of the plug and seat arrangement. The shape of the valve plug determines the flow characteristics of the valve. Different valve characterizations may be achieved by re-shaping the valve trim.

What is CV and KV in control valve?

The Valve Coefficient (Cv – in Imperial unit) – the number of US GALLON PER MINUTE of water at 60 °F that will flow through a valve at specific opening with a pressure drop of 1 psi across the valve. The flow factor (Kv – in Metric unit) – the amount of water that will flow in m3/hr.

What is KV value for valves?

The Kv value is the volume flow of a medium per time unit with a pressure drop of 1 bar at a specific temperature. In practical terms this means that it is only possible to make a statement on the flow rate at a specific opening degree of the valve.

What is KV in control valve?

The Kv value expresses the amount of flow in a regulating valve at a given valve position with a pressure loss of 1 bar. The special situation with a fully open valve determines the Kvs value. The amount of flow at a lower pressure loss (Kv) can be calculated using the formula: Kv = Q / √ΔP.

How do you calculate CV value?

The formula for the coefficient of variation is: Coefficient of Variation = (Standard Deviation / Mean) * 100. In symbols: CV = (SD/x̄) * 100. Multiplying the coefficient by 100 is an optional step to get a percentage, as opposed to a decimal.

What is valve CG?

For a specific gas control valve, the flow coefficient Cg or Kg is determined experimentally by control valve manufacturers, and you can found it in manufacturers technical specifications. You can calculate the gas control valve capacity for given upstream and downstream pressure and known flow coefficient Cg or Kg.

How to design a valve for flow control?

In designing a valve for a particular process, it is important to maintain a linear relationship between lift l l and flow q q. A nonlinear relationship makes flow control tuning more complicated that requires gain scheduling, piecewise linearization in the control software, or other measures to compensate for the nonlinearity.

What is the selection process for control valves?

Assuming no cavitation/flashing/choking then you can take the result and start to select a particular valve. The selection process includes: Pick an acceptable valve body type. (Reciprocating control valves with a digital positioner and a good guide design will provide the tightest control.

What are the key concepts in valve design?

A valve design involves selecting the type of valve, the body size `C_v`, and trim that gives a particular lift function `f(l)`. A few key concepts are important in valve design: Pressure is generated by pumps and dissipated over valves and the system.

What is the function of a control valve?

A control valve is a power operated device capable of modulating flow at varying degrees between minimal flow and full capacity in response to a signal from the controlling system. Control valves may be broadly classified by their function as “on-off” type or “flow regulating” type.