Size it for the flow, not for the line
This is the single most common check valve mistake. A swing check needs enough flow to hold the disc firmly against its full-open stop. Fit a line-sized check valve on a system that normally runs well below design flow and the disc floats somewhere mid-travel, fluttering against the hinge pin with every pressure ripple. The pin and bushing wear out, the disc eventually detaches, and the failure arrives without warning. Give the manufacturer your normal and minimum flow rates and let the valve be sized to those — a check valve one size below the line, with reducers, is a perfectly normal and often correct answer.
Slam is a system problem that you solve at the valve
When a pump trips, the column of liquid downstream decelerates and reverses. A conventional swing check does not begin to close until reverse flow is already established, and the disc then slams onto the seat against a moving column — the bang you hear is a pressure transient that can exceed the rating of the pipework. How bad it gets depends on how quickly your system reverses. On slow-reversing systems a plain swing check is fine. On fast-reversing ones — high-head pumps, long discharge lines, parallel pumps — you need a design that closes before reversal builds: a spring-assisted nozzle check, a dual-plate valve with spring, or a tilting-disc design. Tell the supplier there is a pump trip case; the valve cannot be selected without it.
Orientation and upstream disturbance
Check valves are orientation-sensitive in a way that isolation valves are not. A swing check works horizontally or in vertical upward flow, never in downward flow. A lift or piston check normally requires one specific orientation and will not seat reliably in any other. All of them want undisturbed approach flow: a check valve mounted directly downstream of an elbow, a pump discharge, or a control valve sees a distorted velocity profile across the disc and will flutter even when correctly sized. Allow a straight run upstream where the layout permits it, and state the orientation on the enquiry.
What to include on the enquiry
- Normal, minimum, and maximum flow rate — the basis for sizing the valve
- Installed orientation: horizontal, vertical up, or vertical down
- Whether a pump trip or fast reverse-flow case exists, and how fast the system reverses
- Valve type: swing, dual plate, nozzle, tilting disc, or lift — driven by the two points above
- Seat type, metal or soft, and the leakage class the shutoff must meet
- Governing standard for the duty — API 6D, BS 1868, or API 594 for wafer designs
Material behaviour and standard references on this page are general engineering guidance for grade selection. Confirm the final specification against your line list and the applicable design code for the project.
