How do you determine the correct installation position for a check valve? What’s the difference between installing it before or after a pump, and where is a pre-pump installation suitable? When used in combination with other valves, where should the check valve be placed?

A check valve, also known as a non-return valve, is an automatic valve. It uses the pressure of the flowing medium inside the pipeline to open or close the valve disc. When the flow stops, the disc closes, effectively preventing reverse flow. This plays a vital role in ensuring pipeline safety.

Types of Check Valves by Structure

Check valves can be divided into three main types based on construction: lift check valves, swing check valves, and butterfly check valves.

- Lift check valves come in two subtypes: vertical and straight-through.

- Swing check valves are available in single-disc, double-disc, and multi-disc versions.

- Butterfly check valves include double-disc and single-disc types.

In terms of connection methods, these check valves can be threaded, flanged, welded, or wafer-type.

Where to Install a Check Valve – Before or After the Pump?

The purpose of a check valve is to maintain the correct flow direction inside the pump and ensure normal pump operation. The answer depends on the system configuration:

1. Installed on the suction line (before the pump) – also called a foot valve.

This is used when the pump is installed above the liquid level (negative pressure condition). Without a foot valve, the pump and suction line would be empty, causing the pump to run dry and fail to draw water. The foot valve holds water in the suction line so the pump stays primed.

2. Installed on the discharge side (after the pump) – common when the liquid level is above the pump (positive suction head).

This allows the pump to start and stop without manually closing the discharge valve. In systems with multiple pumps connected to a common header, the check valve prevents reverse flow through idle pumps.

Where to Place the Check Valve Relative to Other Valves?

Typically, the check valve should be installed on the pump discharge, before the discharge isolation valve (such as a gate valve, butterfly valve, or globe valve). This arrangement facilitates maintenance of the check valve.

A common sequence from the pump outlet is:

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

Option 1: Check valve before the gate or 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 bears 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 hammering.

Option 2: Gate or butterfly valve before the check valve

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

Disadvantages: Who protects the check valve? A check valve opens and closes based on pressure differences. If the total header pressure is high, the valve stays closed; if pump pressure is high, it opens. Unstable flow can cause the check valve to cycle repeatedly, reducing its lifespan. Moreover, if a check valve fails – especially in a common-header system – the entire system may need to be shut down for repair.

Since check valves operate frequently and their internal components and seals are prone to wear, they should be installed before the discharge isolation valve to allow easy maintenance without shutting down the entire system. Isn’t that how you usually see it installed?