Many readers ask: where should a check valve be installed? How is its position determined? What is the difference between installing it before or after the pump, and where is pre-pump installation suitable? Check valves are often used together with other valves – so where exactly should the check valve be placed in relation to them? Let’s explore these questions.

What is a check valve?

A check valve (also called a non-return valve) is an automatic valve. It uses the pressure of the flowing medium to open or close the disc. When flow stops, the disc closes, preventing reverse flow and protecting the pipeline system.

Types of check valves by structure

Lift check valves – vertical or straight-through type.

Swing check valves – single disc, double disc, or multi‑disc.

Butterfly check valves – double‑disc or single‑disc type.

Connection methods: threaded, flanged, welded, or wafer‑type.

Where to install the check valve – before or after the pump?

The purpose of a check valve is to maintain the correct flow direction inside the pump. Two typical cases:

Before the pump (suction side) – called a foot valve.

Used when the pump is installed above the liquid level (negative pressure condition). Without it, the pump and suction line would be empty, causing the pump to run dry. The foot valve keeps the pump primed.

After the pump (discharge side) – used when the liquid level is above the pump (positive suction head).

This allows starting and stopping the pump without manually closing the discharge valve. It is especially important in common‑header (multiple pump) systems to prevent reverse flow through idle pumps.

Where to place the check valve relative to other valves?

The check valve should be installed on the pump discharge, before the discharge isolation valve (e.g., butterfly valve, gate valve, globe valve) so that it can be serviced. A typical sequence from the pump outlet is:

Pump → Flexible connector (vibration isolator) → Check valve → Isolation valve (butterfly/gate/globe valve)

Two common arrangements are debated:

1. Check valve first, then gate/butterfly valve

Advantages: The isolation valve protects the check valve – especially in parallel pump systems. When one pump runs while another is shut, the shut pump’s isolation valve absorbs the pressure surge. If the check valve fails, the inlet and outlet valves can be closed to isolate it for repair.

Disadvantages: Who protects the isolation valve? There have been cases where a butterfly valve disc was damaged by water hammer.

2. Gate/butterfly valve first, then check valve

Advantages: The check valve absorbs the hydraulic shock, protecting the isolation valve.

Disadvantages: Who protects the check valve? The check valve opens and closes based on pressure difference. Unstable flow can cause it to cycle repeatedly, reducing its life. Moreover, if a check valve fails in a common‑header system, the entire system may need to be shut down for repair.

In practice, because check valves operate frequently and their internal parts and seals are prone to wear, they are usually installed before the discharge isolation valve for easier maintenance. Isn’t that what you commonly see?

Extended discussion: the correct sequence at the pump discharge

To reduce pump vibration and its impact on valves, the flexible connector (rubber joint) should be placed directly at the pump outlet. The check valve sometimes needs maintenance, so it should be installed before the isolation valve to allow isolation from the system water. A common view is:

Pump → Flexible connector → Check valve → Gate/butterfly valve

Design guidelines mention two scenarios:

Small‑diameter pipes – check valve before gate valve. The gate valve helps protect the check valve from damage.

Large‑diameter pipes – gate valve before check valve. The gate valve is easier to operate (open/close) at large sizes. The check valve’s main role here is to prevent excessive pump reverse speed and avoid flooding the pump house. If the check valve were placed on the suction side, reverse flow after a pump stop would still affect the pump. Also, the suction line should have as few fittings as possible to maintain sufficient NPSH (Net Positive Suction Head).

Why the sequence: flexible connector → check valve → gate valve?

The flexible connector absorbs vibration and is therefore placed at the pump discharge connection.

The check valve operates frequently (every start/stop) and is more likely to need repair. By placing it before the gate valve, you can close the gate valve and repair the check valve without shutting down the whole system.

The gate valve is rarely operated under normal conditions, so it is placed after the check valve.

Where should the pressure gauge be installed?

The pressure gauge should be installed on the pump discharge before the check valve. This protects the gauge from water hammer damage (the check valve absorbs the hammer after it).

Recommended final sequence:

Pump → Flexible connector → Pressure gauge → Check valve → Gate/butterfly valve

Tip from construction practice: If the pump flange does not match the flexible connector directly, use a reducer or a short pipe spool as a transition. Remember that the pump itself is a major vibration source – the flexible connector is the first component to protect the piping system from vibration. This applies to chillers, fans, and other rotating equipment as well.