If you have a ratio that is higher than 2:1, you risk cavitation which again could have adverse effects on the system such as causing undesired noise and damaging the PRV seal.

Eliminating air from the system minimises the associated consequences of pressure surges, friction loss, corrosion, and vibrations.

For example, as shown in the section diagram below, if you have a PRV in the ceiling and set the outlet pressure to 500 kPa, when the water gets to the outlet 2m below, the pressure will be approximately 520 kPa due to the vertical pressure gain. This consequently means that there is too much pressure at the fixture and that could lead to a non-compliant system and damaged tapware.

MuellerSteam Specialty

The diagram below is useful for checking the inlet and outlet pressure of the PRV design to see if it falls in the ‘normal operating conditions’ area.

You can then plot the peak flow rate on the graph and find the corresponding PRV size. As a rule of thumb, you want to be within the 1-2 m/sec zone on the chart.

For example, if you have hot water passing through a PRV at a high velocity on a regular occasion, it would be prudent to select a stainless steel PRV. Alternate material selections could cause corrosion of the valve.

MuellerYStrainer

CASE STUDIES Salon Republic, USA "The quality of the designs saw significant improvement with the adoption of h2x." "The software offers precision through detailed result outputs and advanced options for efficient pipe sizing, allowing heating engineers to optimise based on parameters like maximum velocity and pressure drop." Read the full case study

"The software offers precision through detailed result outputs and advanced options for efficient pipe sizing, allowing heating engineers to optimise based on parameters like maximum velocity and pressure drop."

"I would estimate over the length of this project, I have spent 50% less time designing than I would on our previous software.

CASE STUDIES Award-Winning Heating Design "Using h2x was pivotal, allowing for precise heat loss calculations, pipe sizing and flow rates for each room. This level of detail ensured that the heating load accurately matched each space's requirements, minimising energy waste and maximising comfort. The strategic placement of heat pumps and careful sizing of pipework were crucial in maintaining minimal pressure drops over an 18-metre distance." Read the full case study

It is important to be aware of this in the design because 80kPa pressure loss could be the difference between supplying a compliant pressure at the fixture and a non-compliant pressure at the fixture.

Setting the bypass PRV to a higher pressure allows the low flow rates to take the path of least resistance and this allows the bypass PRV to be used during the non-peak demand.

This level of detail ensured that the heating load accurately matched each space's requirements, minimising energy waste and maximising comfort.

It is important to size a pressure reduction valve (PRV) to suit the flow rate that passes through it. You should not necessarily match the inlet pipe size as this can lead to over-sizing of the PRV and oversizing the PRV has adverse effects on the system such as causing undesired noise and also damaging

MUELLER Strainergasket

CASE STUDIES Greengate, UK "I would estimate over the length of this project, I have spent 50% less time designing than I would on our previous software. The ability to output the design straight into Revit assisted clash detection and coordination." Read the full case study

If you did need to reduce the pressure at a higher ratio such as from 1200 kPa to 300 kPa (4:1), installing an additional PRV in series is recommended as shown in the example below. This allows a 2:1 ratio to be maintained through each PRV.

As a rule of thumb, the PRV bypass should be designed for 20% of the peak flow rate and need to be set at least 50 kPa above the primary PRV.

It is important to size a pressure reduction valve (PRV) to suit the flow rate that passes through it. You should not necessarily match the inlet pipe size as this can lead to over-sizing of the PRV and oversizing the PRV has adverse effects on the system such as causing undesired noise and also damaging the PRV seal.

To size the PRV correctly, you need to find the technical data sheet from your preferred manufacturer and find a table that looks similar to below.

The strategic placement of heat pumps and careful sizing of pipework were crucial in maintaining minimal pressure drops over an 18-metre distance."

Buildings rarely operate at a peak demand so they are not commonly subject to the peak flow rate. Neglecting the low flow rates will also have adverse effects on the system such as causing undesired noise and damaging the PRV seal.