Practical engineering guide

Specifying valves and actuators

Nominal size and pressure rating are only the starting point. A valve must suit the medium, actual pressure conditions, control arrangements and process function, including its behaviour during a fault.

Isolation and control have different purposes

An isolation valve interrupts flow according to its required function and leakage performance. A control valve must operate appropriately across the requested flow range. Size, flow coefficient and characteristic follow from process data. An oversized valve may control poorly; matching the pipe diameter is not automatically the right selection.

Assess the system, not only the body

Upstream and downstream pressures, temperature, phase and fluid properties matter. Cavitation, flashing with vapor persisting downstream, or abrasive particles can change construction and material requirements. The actuator must suit the required force or torque, available energy and safe state. Excessively rapid closure can adversely affect the pressure dynamics of the system.

Agree verification and interfaces

Specify connections, face-to-face dimensions, orientation, indication and control interfaces. Seat leakage and body integrity are separate requirements. Tests and their scope are agreed for the application. A material name alone does not demonstrate suitability for a particular chemical composition and temperature. Engineering should therefore define the complete assembly, not simply a valve part number.

Expected engineering outputs

Valve, actuator and accessory specification.
Confirmed operating limits and control requirements.
Agreed assembly tests and handover documents.

Technical sources and further reading

Reviewed on 18 October 2026. Product limits and applicable requirements are confirmed for each specification.

Selection in context

Selecting a valve by its required function

First define control, isolation or reverse-flow prevention, then evaluate the valve, actuator and all operating conditions together.

On a small screen, scroll the table sideways to compare the selection criteria.

Selecting a valve by its required function
Principle or option	Typical application	What to verify when selecting
Globe control valve	Continuous flow, pressure or temperature control through an adjustable flow area.	Kv/Cv at operating points, characteristic, cavitation or flashing, noise, shut-off leakage and actuator thrust.[1][2]
Ball valve	Quarter-turn pipeline isolation; throttling requires a design intended for control duty.	Bore and pressure loss, seats and seals, torque, cycling frequency and required position on loss of power.[3][2]
Butterfly valve	Compact isolation or control where face-to-face length and weight are important.	Design and seat type, permitted differential pressure, disc clearance, shut-off leakage and torque throughout travel.[3][2]
Check valve	Automatic reverse-flow prevention, for example on a pump discharge.	Opening conditions, flow range, orientation, pressure loss and response to rapid flow changes.[4]

Sources for this comparison

Reviewed on 18 October 2026. Selection is confirmed for the specific operating conditions and equipment design.

Before we start

Questions that shape the project.

Is the existing nameplate enough for a replacement?

It helps, but include actual operating conditions and the reason for replacement. The original valve may have operated outside its suitable range, or the process requirements may have changed.

Does a closed valve always mean zero leakage?

Not without a defined specification. Required tightness, medium, direction and verification conditions must be agreed. The role of a valve in safely isolating equipment also needs separate assessment.

Your next project

A clear brief.
A practical next step.

Send your drawings, operating parameters or a short description of the change you need. We will review the technical interfaces and propose the next steps towards a quotation, clarifying any missing information with you.

Discuss your requirements ↗Prepare a technical brief →+420 731 771 147 info@emkoproject.cz