Pressure control valves play a crucial role in water services particularly where the pressure supplied from the property service or pumps exceeds 500 Kilopascals (kPa).

This article aims to provide an in depth understanding of pressure control valves their importance features types of installations and methods for selecting the appropriate valve and size.

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According to AS/NZS 3500.1:2018 clause 3.3.4 the water at any outlet within a building excluding a fire service outlet should not exceed a static pressure of 500 kPa.

If the delivery from the Water Services Provider’s water main or internal design pressures surpasses this maximum pressure it becomes necessary to install break tanks, pressure ratio or pressure reducing valves. These devices help maintain the desired pressure within a building’s water supply.

Importance of Pressure Reduction

Maintaining the maximum pressure requirement is essential because pressures above 500 kPa can lead to several issues in water supplies including:

  • Failure of piping, appliances, apparatus and taps
  • Property damage
  • Excessive noise in the water supply system
  • Loss of water

Features of Pressure Control Valves

Pressure control valves are integral components in water services particularly in systems where the pressure exceeds 500 Kilopascals (kPa). These valves come in two main types: pressure reducing valves and pressure limiting valves each with its unique features and applications.

Pressure Reducing Valves

Pressure reducing valves are designed to lower the incoming water or fluid pressure to a setting that can be adjusted by the user within a range of 100 Kpa – 600 Kpa. This adjustable nature allows for greater flexibility and control making them suitable for a variety of applications.

One of the key features of pressure reducing valves is their diaphragm design. This design allows the valve to respond more accurately to changes in the inlet pressure ensuring a consistent outlet pressure even when the inlet pressure varies. This accuracy is crucial in preventing potential damage to plumbing systems and appliances caused by pressure fluctuations.

Another important feature of pressure reducing valves is their ability to prevent downstream creep. Downstream creep occurs when the pressure downstream of the valve increases when there is no flow, which can lead to excessive pressure in the system. Pressure reducing valves are designed to prevent this contributing to their reliability and efficiency.

Furthermore pressure reducing valves are serviceable, meaning they can be repaired or maintained without needing to be completely replaced. This feature can lead to cost savings over time as well as less downtime in the event of a valve failure.

Pressure Limiting Valves

Pressure limiting valves on the other hand are non adjustable. They are designed to limit the pressure to a preset level regardless of the inlet pressure. This makes them less flexible than pressure reducing valves but they can still be effective in systems where the inlet pressure is relatively stable.

Pressure limiting valves feature a piston design which is simpler and more robust than the diaphragm design of pressure reducing valves. However this design makes them less accurate with varying inlet pressures which can be a disadvantage in systems where the inlet pressure fluctuates.

One of the drawbacks of pressure limiting valves is their tendency to creep on downstream under no flow conditions. This can lead to an increase in pressure downstream of the valve of as much as 30% which can potentially cause issues in the system.

Another important point to note about pressure limiting valves is that they are non serviceable. This means that if a pressure limiting valve fails or requires maintenance it must be completely replaced. While this can lead to higher costs and more downtime in the event of a valve failure the robust design of these valves means they are generally quite reliable.

Types of Installations

Valve installations can be categorized into three types:

  • Single regulator valves
  • Multiple regulators installed in series
  • Parallel regulators installed in parallel
  • Single regulator installations are most commonly used in residential applications. These installations require the regulator to maintain a reduced static pressure with all demand flows from zero to full capacity.
  • Multiple regulator installations in series are used in special situations where a wide variance between the inlet pressure and the desired reduced pressure exists. This type of installation is generally considered when the reduction is more than a four (4) to one (1) ratio.
  • Parallel installations involve a group of parallel regulators all receiving water from a common source. After flowing through the chain of valves water enters a common service line of sufficient size to service the system at the reduced pressure. As demand in the system increases the larger valves come into service.

Choosing the Right Pressure Control Valve and Its Size

Picking the right pressure control valve and its size is a vital task that involves a few key steps. This procedure ensures that the chosen valve will work efficiently within the system, maintaining the desired pressure and avoiding potential problems related to excessive pressure.

Determining the Required Flow

The initial step in choosing the right valve and size is to determine the flow needed for the application usually measured in liters per second. The flow rate is calculated based on the total demand of all outlets that the system will service.

This encompasses all appliances, fixtures and outlets that will utilize water. It’s crucial to take into account the maximum simultaneous demand when figuring out the flow rate.

Figuring Out the Maximum Allowable Difference

The third step is to figure out the maximum allowable difference between the flowing pressure and the static pressure also known as the rate of Fall off.

The static pressure is the pressure in the system when no water is being used while the flowing pressure is the pressure when water is moving through the system.  The difference between these two pressures, should be minimised to ensure a consistent and reliable water supply.

Gauging the Delivery Pressure

The  subsequent step is to gauge the delivery pressure of the water measured in kilopascals.

This is the pressure at which the water will be transported from the source to the system.

It’s worth noting that this pressure can fluctuate based on several factors such as the height difference between the water source and the delivery point the distance the water needs to travel and the size and condition of the pipes

Utilizing the Information on Flow Charts

The final step is to utilise all this information on appropriate flow charts. These charts often provided by valve manufacturers assist in determining the type and size of valve that best suits the installation’s needs.

The charts typically contain information about the valve performance under various conditions and can guide you in selecting a valve that will perform optimally under your specific conditions.

Thermal Expansion

A backflow prevention device or check valve installed in a water supply line can create a closed system. This can lead to excessive pressures in the heated water lines when the thermally expanded water has no means of escape.

The pressure build up occurs as the heated water expands in volume due to a rise in temperature. In Western Australia the fitting of an expansion control valve on storage water heaters is a mandatory requirement. The expansion valve will relieve the built up pressure during the heating cycle.


Pressure control valves are essential components in water services especially when dealing with high pressures. Understanding their features, types and the methods for selecting the appropriate valve and size is crucial for maintaining a safe and efficient water supply system.

When selecting valves for controlling pressures in water services consideration should be given to matching the particular operation required to the characteristics of valves available. Valves should then be installed and tested to manufacturer’s specifications and relevant Australian Standards.