Oilfield check valves explained: dart, swing and wafer checks, and drill pipe float valves

Pumps stop, lines fail and wells kick. In each case fluid wants to run the wrong way, back towards equipment and people. A check valve is the part of the line that lets flow through in one direction only, and the oilfield uses several kinds, each suited to where it sits — in the treating iron, at a flanged connection, or deep in the drill string above the bit.

/01Dart, swing and wafer.

/02Dart and swing checks on treating iron.

A dart check holds a dart against its seat with a spring; forward flow pushes it open and the spring and any reverse flow push it shut, so it closes quickly and positively. A swing check hangs a flapper on a hinge that forward flow swings out of the way, giving a straighter path through the valve. On our listings the dart checks have F6NM darts with 316 stainless or, for sour service, Inconel 625 body inserts; the 1502 swing checks have 316 stainless discs on 17-4PH hinges. Union-ended checks take the rating of their figure — see hammer union figure numbers.

/03Flanged and wafer checks.

Where a check sits at a flanged connection — at a wellhead outlet or in a permanent manifold — it is usually a flanged body or a wafer between two flanges. Our Type R wafer checks are API 6A, in 3-1/16" at 10,000 and 15,000 psi and 3-1/8" at 5,000 psi, at PSL 1 or PSL 3 and PR1, most with F6NM discs and Inconel 625 overlay seats. For process piping, the ASME raised-face swing checks are rated by class to API 6D: 3" Class 150 at 285 psi and 3" Class 600 at 1,480 psi, both sour service.

/04Drill pipe float valves.

A float valve sits in a recess in the float sub or bit sub, just above the bit, and stops mud, cuttings and well fluid flowing back up the drill string. Model G is a flapper valve and Model F a plunger valve; the ported versions, GA and FA, have a small port through the valve. Each size is made for a sub recess: the valve OD, length and baffle-plate recess must match the sub, which is why our listings give all three alongside the connections the sub is cut for. The listings give a 7,500 psi working pressure for Model F and G valves.

/05Installing and ordering.

Every check valve has a flow direction, marked on the body; one installed backwards blocks the line or, worse, fails to protect it. For treating-line checks, give the type, size, end figure and gender, and the service. For float valves, give the size or the float sub connection and recess, and the model — flapper or plunger, ported or plain. The rest of the treating line is covered in flow iron explained.