What Is a Control Valve? Types and Testing

A control valve is a valve that manages the flow, pressure or direction of a fluid by opening, closing or partly obstructing the flow path, usually in response to a signal from a controller. Common types of control valves include globe, ball and butterfly valves in process piping, and directional, pressure and flow control valves in hydraulics. Control valve testing checks how much fluid a valve passes (its Cv or flow coefficient), how it leaks, and how accurately and quickly it responds.

What is a control valve?

In process industries, the control valve is the final control element: a controller compares a measured value such as flow or level with a set point and moves an actuator that positions the valve. In hydraulic systems the term is broader and covers directional, pressure and flow valves that steer and limit oil to cylinders and motors. In both cases the job is the same: to control where fluid goes and how much of it goes there.

Types of control valves

Control valve types are usually grouped by function or by valve body design.

By body design (process and industrial valves):

Globe valves: a plug moves against a seat, giving good throttling control and tight shut-off.
Ball valves: a ball with a bore rotates through a quarter turn; used for on/off duty and in some throttling designs.
Butterfly valves: a disc rotates in the flow path; compact and economical for larger line sizes.

By function (hydraulic control valves):

Directional control valves: start, stop and change the direction of oil flow, typically with a spool or poppet.
Pressure control valves: limit or set pressure; examples are relief, reducing and sequence valves (see pressure relief valve).
Flow control valves: set actuator speed by restricting flow, sometimes with pressure compensation.
Proportional and servo valves: position the spool in proportion to an electrical signal for smooth, accurate control of flow or pressure; servo valves respond faster and are used where precision is critical.

Flow coefficient: Cv and Kv

The flow coefficient describes how easily a valve passes fluid. Cv is the number of US gallons of water per minute that flows through the valve at 60 °F with a pressure drop of 1 psi across it. Kv is the metric equivalent: cubic metres of water per hour at a pressure drop of 1 bar. The two are related by Kv ≈ 0.865 × Cv. A higher Cv means a larger flow for the same pressure drop, so Cv is what engineers use to size a control valve.

How control valves are tested

Control valve testing usually combines several measurements on a test rig:

Flow and pressure drop across the valve at set openings, which gives the flow coefficient and the valve characteristic.
Leakage: internal leakage through the closed valve and external leakage to the outside.
Pressure strength: a hydrostatic or proof test of the body.
Response and accuracy: for proportional and servo valves, step response, dead band, linearity and hysteresis.
Endurance: repeated cycling to check wear over life.

More detail on valve test parameters is in the hydraulic valve testing glossary.

Control valve test rigs from Neometrix

Different valves need different rigs. The CV and control valve test rig page describes a system for flow coefficient (Cv/Kv), pressure drop and flow-rate testing of control valves from DN65 to DN350, up to 550 m³/hr. For hydraulic valves, the hydraulic control valve test bench is a 350 kW automated bench rated to 400 LPM and 420 bar for mobile and industrial valves, while the control valve test rig for automobile valves simulates lift, lower and hold loads at 46 LPM and 250 bar. The hydraulic control valve test bench for steel plants page describes a universal rig for testing valve types under controlled hydraulic conditions, and the valve test rig covers hydrostatic and seat-leakage testing of butterfly and check valves.

Frequently asked questions

What is a control valve?

A control valve is a valve that regulates the flow, pressure or direction of a fluid by opening, closing or partly blocking the flow path, usually in response to a control signal.

What are the main types of control valves?

In process piping the common body types are globe, ball and butterfly valves. In hydraulics, control valves are grouped by function into directional, pressure and flow control valves, with proportional and servo valves used for precise control.

What is Cv in a control valve?

Cv is the flow coefficient: the US gallons per minute of water at 60 degrees F that pass through the valve with a 1 psi pressure drop. Its metric counterpart Kv uses cubic metres per hour and a 1 bar drop.

How is a control valve tested?

On a test rig, using measured flow and pressure drop to establish the flow coefficient, together with leakage, pressure-strength and, for proportional or servo valves, response and hysteresis checks.

Why do control valves need to be tested?

Valves wear, leak and drift out of tolerance. Testing confirms they pass the intended flow, seal properly and respond accurately before installation or after overhaul.

For valve test requirements or a quotation, contact the Neometrix team. You can also see our hydraulic test bench manufacturer profile.