Automatic control valves are the unsung heroes of water infrastructure. From maintaining consistent water pressure to controlling flow, protecting pipelines and managing reservoir levels, these valves work quietly in the background to keep water networks operating efficiently.

But like any mechanical equipment, things can occasionally go wrong.

Whether you’re dealing with a pressure reducing valve that won’t open, a valve that refuses to close, or a system experiencing pressure fluctuations, understanding the basics of how these valves operate can make troubleshooting much easier.

At Total Flow Control (TFC), we regularly assist water authorities, councils and industrial operators with diagnosing, repairing and maintaining automatic control valves.

The good news? Many common issues are relatively straightforward to identify, and not every problem requires a complete valve overhaul.

How Does an Automatic Control Valve Work?

Before diving into troubleshooting, it helps to understand the basic operating principles.

Most diaphragm-operated automatic control valves use the pressure of the water flowing through the pipeline to control their operation. They don’t necessarily require electricity or an external power supply.

Instead, they rely on a hydraulic control system consisting of a main valve, diaphragm, bonnet (also known as the cover or control chamber), and a series of pilots and associated fittings.

The basic principle is simple:

• To close the valve: Water is directed into the bonnet, increasing pressure above the diaphragm and forcing the valve towards its closed position.
• To open the valve: The pilot system allows water to flow out of the bonnet, reducing pressure above the diaphragm and allowing inlet pressure to lift the valve open.
• To regulate the valve: The pilot system continuously controls the flow of water into and out of the bonnet, allowing the main valve to modulate and maintain the required pressure, flow or level.

In simple terms, water entering the bonnet closes the valve, while controlled water leaving the bonnet allows it to open.

The pilot system is essentially the brains of the operation.

Depending on the application, the valve may be configured for pressure reducing, pressure sustaining, pressure relief, rate-of-flow control, level control or a combination of these functions.

Although the operating principles are similar, the pilot arrangements and control requirements can vary significantly.

Common Automatic Control Valve Problems and How to Troubleshoot Them

When an automatic control valve stops behaving as expected, it’s tempting to assume there’s a major mechanical problem.

However, experience tells us that many faults originate in the smaller components of the pilot system rather than the main valve itself.

Here are some of the most common problems and where to start looking.

1. The Valve Won’t Open

If your automatic control valve is remaining closed when it should be opening, there are several things worth checking before considering dismantling the main valve.

Check the isolation valves

Start with the obvious. Are the small ball valves in the pilot system open?

These valves are sometimes closed during maintenance and accidentally left in the wrong position.

Also confirm that the main upstream and downstream isolation valves are correctly positioned and that adequate inlet pressure is available.

Check the pilot adjustment

An incorrectly adjusted pilot can prevent the main valve from opening as intended.

For example, on a pressure reducing valve, an incorrectly set pressure reducing pilot may restrict the release of water from the bonnet, keeping the main valve closed.

Check the pilot setting against the required operating conditions and manufacturer’s instructions.

Inspect the flow stabiliser

Some valves are fitted with a flow stabiliser, such as the Singer Model 26.

If the stabiliser is incorrectly adjusted or blocked, it may restrict the flow of water leaving the bonnet and prevent the main valve from opening correctly.

Check for blockages in the pilot system

Small pilot lines, fittings and internal passages can become blocked by sediment, scale or debris.

If water cannot escape from the bonnet through the pilot circuit when required, the valve may remain closed.

TFC Tip: Before pulling the main valve apart, establish whether the pilot system is allowing water to discharge from the bonnet. This can help narrow down whether the problem is hydraulic or mechanical.

2. The Valve Won’t Close

A valve that remains open when it should be closing can cause excessive downstream pressure, uncontrolled flow or other operational issues.

Check the supply of water to the bonnet

Remember, the valve relies on water entering the bonnet to close.

If there is insufficient pressure or a restriction preventing water from entering the bonnet, the valve may be unable to close.

Check the pilot supply lines and associated fittings for restrictions.

Inspect and clean the strainer

One of the most common problems we encounter is a blocked pilot strainer.

These strainers protect the small internal passages of the pilot system from debris circulating through the pipeline.

Over time, sediment, rust particles and other contaminants can accumulate and restrict water flow.

A blocked strainer can prevent sufficient water from reaching the bonnet, resulting in a valve that won’t close correctly.

Check the pilot valve

A faulty pilot may continuously allow water to discharge from the bonnet, preventing the pressure required to close the main valve from developing.

Damaged pilot diaphragms, worn internal components or incorrect adjustments can all contribute to this problem.

Inspect the main valve diaphragm

If the pilot system is operating correctly but the main valve still won’t close, a damaged main diaphragm may be the cause.

A torn or deteriorated diaphragm can prevent the valve from maintaining the hydraulic pressure differential required for correct operation.

Check for mechanical obstructions

Debris trapped between the valve disc and seat, or an obstruction preventing the stem from travelling freely, may stop the valve from closing completely.

Worn or damaged seating surfaces can also cause leakage even when the valve has reached its closed position.

3. The Valve Is Hunting or Experiencing Pressure Fluctuations

One of the more frustrating problems with automatic control valves is hunting.

This occurs when the valve continually opens and closes in response to changing pressure conditions, rather than maintaining a stable operating position.

The result can be fluctuating downstream pressure, excessive valve movement and unnecessary wear on internal components.

Check for trapped air

Air trapped inside the bonnet or pilot system can affect the hydraulic response of the valve.

Because air is compressible, it can introduce delays and instability into the control system.

Check the appropriate air bleed points and ensure trapped air is removed in accordance with the manufacturer’s procedures.

Inspect the flow stabiliser

Flow stabilisers, such as the Singer Model 26, are designed to help control the response of the main valve.

If incorrectly adjusted, the valve may respond too aggressively or too slowly to changes in demand.

Correct adjustment can significantly improve stability.

Check the pressure sensing line

Some pilot arrangements use external pressure sensing lines.

If these are installed too close to bends, fittings, valves or other sources of turbulence, the pilot may receive an inconsistent pressure signal.

This can result in the valve continually correcting itself.

Consider the operating conditions

It’s also important to check whether the valve is correctly sized for the application.

A valve operating at extremely low flows relative to its capacity may struggle to maintain stable control.

Similarly, rapid changes in demand, excessive pressure differentials or cavitation can contribute to unstable operation.

Sometimes the issue isn’t a faulty valve at all, but rather the conditions it’s being asked to operate under.

4. The Valve Is Responding Too Slowly

Not every fault involves a valve that completely stops working.

Sometimes a valve opens or closes, but takes much longer than expected.

This can be particularly problematic in applications requiring quick responses to changing system conditions.

Common causes include:

• Partially blocked pilot lines or strainers.
• Incorrectly adjusted opening or closing speed controls.
• Restricted flow through pilot components.
• Air trapped within the hydraulic control system.
• Incorrect pilot configuration or settings.

Many automatic control valves incorporate adjustable needle valves or speed controls to regulate how quickly water enters or leaves the bonnet.

These adjustments should be made carefully, as an excessively fast response can introduce pressure surges or water hammer into the system.

The objective is to achieve a stable, controlled response appropriate for the application.

5. The Valve Is Leaking or Passing Water When Closed

If a valve appears to be closed but water continues to pass through it, the issue may be mechanical rather than related to the pilot system.

Possible causes include:

• Debris lodged between the disc and seat.
• Worn or damaged seat seals.
• Damage to the valve disc.
• An obstruction preventing full stem travel.
• Insufficient bonnet pressure to achieve complete closure.

Before assuming the seating components have failed, confirm that the valve is actually receiving the hydraulic pressure required to close fully.

If the pilot system is functioning correctly and the valve continues to pass water, an internal inspection may be necessary.

Don’t Overlook the Small Components

One of the biggest lessons we’ve learnt from working with automatic control valves is that a small problem in the pilot system can create a big problem in the main valve.

A blocked strainer, damaged pilot diaphragm or incorrectly adjusted flow stabiliser can make a perfectly serviceable valve appear to have completely failed.

In many cases, these issues can be identified without removing the entire valve from the pipeline.

Regular inspections, cleaning and maintenance of the pilot system can significantly improve reliability and reduce unexpected downtime.

A Simple Troubleshooting Checklist

Before arranging major repairs or replacing an automatic control valve, consider the following:

1. Check the operating conditions. Is there adequate inlet pressure, and are the upstream and downstream isolation valves correctly positioned?
2. Check the pilot isolation valves. Are they in their correct operating positions?
3. Inspect the strainer. Is it clean and allowing adequate water flow?
4. Check the pilot settings. Are they appropriate for the required operating pressure or control function?
5. Inspect the flow stabiliser and speed controls. Are they correctly adjusted and free from restrictions?
6. Check for trapped air. Has the bonnet and pilot system been properly bled?
7. Check the hydraulic control circuit. Is water able to enter and leave the bonnet as required?
8. Consider the main valve internals. Could a damaged diaphragm, worn seat or mechanical obstruction be causing the issue?

These checks can help identify where the problem may be occurring and whether further investigation is required.

Important: Automatic control valves can operate under significant pressure. Before disconnecting pilot lines, opening fittings or dismantling components, ensure the system is safely isolated, depressurised and maintained in accordance with site procedures and the manufacturer’s instructions. Changes to pilot settings or isolation positions can affect network pressures and should only be undertaken by authorised, competent personnel.

Preventative Maintenance Makes All the Difference

Like any critical piece of infrastructure, automatic control valves benefit from regular preventative maintenance.

Unfortunately, because these valves often operate reliably for years without attention, they can easily be forgotten until something goes wrong.

A routine maintenance program should include inspection of pilot components, cleaning strainers, checking diaphragm condition, verifying setpoints and confirming correct valve operation.

For critical applications, periodic functional testing can help identify developing problems before they result in an unexpected failure.

Need Help With an Automatic Control Valve?

At Total Flow Control, we don’t just supply automatic control valves. We also understand how they operate and what can go wrong in real-world applications.

Our team can assist with:

• Troubleshooting and fault diagnosis.
• On-site valve inspections and assessments.
• Pilot system repairs, replacements and modifications.
• Valve servicing, refurbishment and spare parts.
• Pressure reducing, sustaining, relief and flow control applications.
• Valve commissioning and performance optimisation.
• Technical support and operator training.

Whether you’re working with a Singer, Bermad or another automatic control valve, we can help identify the issue and work towards a practical solution.

Sometimes it’s a simple adjustment. Sometimes it’s a blocked strainer. And sometimes the valve just needs a little more attention.

Whatever the problem, we’re here to help get your system operating as it should.

Total Flow Control – Valves | Actuators | Controls

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