Whatever the application, the types of check valves in this guide all share a single job: stop reverse flow. They do that with no actuator, no power supply and no control signal, which is why a check valve sits on pump discharge lines, compressor outlets, header connections and anywhere a backflow event would damage equipment or contaminate a product stream.
The trouble is that “a check valve” is not a design, which is why the types of check valves are so often confused. Four distinct mechanisms carry that name, and they close at completely different speeds. Choosing the wrong one is the most common cause of water hammer incidents and repeated check valve failures on the same line.
The four types of check valves, and what each one does
Swing check valve
A disc hinged on a pin above the flow path swings open under forward flow and drops back onto the seat when flow reverses. It offers a nearly unobstructed bore, so pressure drop is minimal — the lowest of the four in most sizes.
Its weakness is closing speed. The disc has to travel through its full arc, and on a large valve with a high flow velocity, the reverse flow is already substantial by the time the disc reaches the seat. That late closure is the classic source of a pressure surge. Some designs add a lever and weight, or an external dashpot, to slow the final travel and control the closure — effective, but it takes up space and needs maintenance.
Best for: horizontal lines with clean media, larger sizes, low-cycling duty, pump discharge where a surge analysis confirms the closure is acceptable.
Dual plate check valve
Two spring-loaded half-discs, hinged at the centre. Because each disc travels a short arc, closing is fast and the valve can be far more compact — a wafer version fits between two flanges with a short face-to-face and a fraction of the weight of a swing check.
The trade-off is a slightly higher pressure drop and a cracking pressure set by the spring, so the valve needs a small differential to open. Soft seats are available and give good tightness in clean service.
Best for: space-constrained installations, retrofits, moderate sizes, and services where fast closure reduces surge. This is the most widely used of the types of check valves in new plant piping. Wafer and lug designs are common under API 594.
Lift check valve (piston or disc type)
The disc or piston lifts vertically off a seat, guided by the body. Flow must change direction, so pressure drop is the highest of the four. In exchange, the guided short stroke produces fast, well-controlled closure.
Best for: small bore lines, high-pressure clean service, vertical installations where a swing or dual plate design cannot be used. The piston variant is widely used on steam and condensate lines.
Axial flow (nozzle) check valve
A spring-loaded disc moves along the axis of the body with the flow, guided by a cage. The flow path remains essentially straight. Closure is the fastest of the four because the stroke is very short and the spring is always acting.
Best for: reciprocating compressor discharge, high-cycle duty, and critical services where surge cannot be tolerated. It is the most expensive of the types of check valves, and normally specified only when the surge analysis demands it.
Comparing the four types of check valves
| Design | Pressure drop | Closing speed | Space required | Orientation limits | Relative cost |
| Swing check | Lowest | Slowest | Longest face-to-face | Horizontal preferred; vertical only in upward flow | Low |
| Dual plate | Low to moderate | Fast | Very short (wafer) | Horizontal or vertical | Moderate |
| Lift / piston | Highest | Fast | Medium | Vertical flow required for piston types | Low to moderate |
| Axial / nozzle | Low | Fastest | Medium | Horizontal, generally | High |
Water hammer: what actually causes it
When a pump trips, the flow in the discharge line decelerates and then reverses. A check valve closes at some point during that reversal. The volume of reverse flow that passes through the valve before it seats determines the magnitude of the resulting pressure surge.
Three things reduce the surge:
- A shorter, lighter closure element— this is why dual plate and axial designs produce smaller surges than a large swing check.
- A springthat starts closing the moment forward flow decays, rather than waiting for full reversal.
- Correct placement— installing the check valve close to the pump discharge minimises the length of pipe that can reverse before the valve seats. Moving a check valve 30 metres downstream instead of 3 metres downstream can multiply the surge.
If a line has a history of check valve failures, the sequence to check is: was a surge analysis done, is the valve in the right location, is the closing mechanism appropriate for the flow velocity, and is the valve sized for the actual operating range rather than the line size.
Sizing: the mistake that hides behind “same size as the pipe”
A check valve that is too large for the actual flow rate opens only partially. The disc or plates then sit in the flow stream, fluttering, wearing the hinge pin and the seat. This is the most common cause of premature failure, and it is invisible in the specification because the size matches the pipe.
Check the actual flow velocity range, not only the nominal flow. Most manufacturers publish a minimum velocity for stable operation of each of the types of check valves they produce. Line size alone is not enough information.
Standards and materials
- API 594covers flanged, lug, wafer and butt-welding check valves.
- API 6Dapplies where the valve is part of a pipeline system and carries the associated testing and documentation requirements. Our API 600 vs API 6D comparison explains how to tell which applies to your line.
- ISO 5208 / API 598define the shell and seat test acceptance criteria, covered in detail in our pressure testing guide.
- Materials follow the medium: cast iron or ductile iron for water, WCB and 13Cr trim for general hydrocarbon service, CF8M and duplex for corrosive streams. Low-temperature service requires LCB or an austenitic body with impact-tested material.
Non-slam behaviour is not a material property. Across all four types of check valves, it comes from the design, the spring and the location — not from a harder seat.
Selection checklist
- What is the actual flow velocity range in normal, minimum and maximum operation?
- Is the medium clean, or does it contain solids that can bridge the seat?
- What happens if the valve closes late — is there a pressure surge the system can absorb?
- How much face-to-face length is available?
- What orientation is available, and does the chosen design accept it?
- What leakage rate is acceptable in the reverse direction, and against which standard?
Question three is the one that decides between a cheap valve and an appropriate one. On a small clean water line with a short discharge, a swing check is fine. On a long pumping main with a high head, it is not.
Frequently asked questions
Does a check valve guarantee zero backflow? No. Every design relies on flow reversal to seat. Small volumes of reverse flow always pass before closure, and leakage rates are defined by the applicable standard.
Can a check valve be installed vertically? Swing and dual plate designs can, provided the flow is upward. Piston lift designs require specific orientation for gravity to assist closure. Confirm against the manufacturer’s instructions for the specific design.
How do I reduce the noise from a check valve? Persistent noise and vibration usually means the valve is undersized for the flow and the closure element is fluttering in a partially open position. Change the size or the design, rather than adding damping.
Should a check valve be used as a block valve? No. It is not a positive isolation device and must never be treated as one for maintenance isolation.
How often should check valves be inspected? Pump discharge and compressor check valves on critical service should be reviewed at each major turnaround. Hinge pin wear, seat damage and spring degradation are the items to inspect.
Send us the line size, medium, flow range and an indication of the pump or compressor characteristic. We will recommend a design and confirm the velocity range it will operate reliably in.
