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Getting pressure right for all floors

As high-rise buildings are becoming a more prevalent sight on UK horizons, it is important to recognise the additional challenges that engineers face as buildings get taller 

Supplying sufficient water pressure to all floors within high-rise buildings has always been a challenge which engineers have had to overcome through careful design. The design should aim to maintain an even distribution of water to all floors, as well as combatting the effect of gravity and ensuring the higher floors still receive adequate water pressure. 

Due to the sheer height of many high-rise buildings, it is common that the municipal water supply pressure will not be adequate to meet the needs of the building; these buildings will often require a pressure-boosting system, this would typically be in the form of booster pump sets or elevated storage tanks. Without a pressure-boosting system, the higher floors within the system may receive low water pressure and during peak times all occupants may experience this issue.

Pressure-boosting systems will increase the pressure of the water to a level that will ensure all floors within the high-rise receive water at an adequate pressure, even during times of high demand. However, whilst solving one problem, pressure-boosting systems, and the subsequent high pressure, can create further issues. 

The use of a pressure-boosting system will increase the water pressure within the pipework significantly, often meaning that standard rated pipes, valves, pumps and fittings may not be sufficient. Careful design will ensure that the right products are specified from the beginning, therefore reducing wastage and time. Since the introduction of BIM into the building services industry, it has become easier to flag potential issues at the very early stages, especially in relation to sizing and flow, thus ensuring all of the products are compatible before the installation stage. 

If parts are installed that are not capable of operating at such a high pressure, the water pressure may cause damage to the pipes, valves and fittings and potentially cause leaks. 

High pressure flowing through pipework within a building can also cause issues for the occupants: cavitation or water hammer can be responsible for causing excessive vibrations and noisy pipework, increased water bills from excessive water wastage, and more frequent maintenance and replacement of fixtures and fittings as a result of the quicker deterioration caused by the high pressure.

Many high-rise buildings require working system pressures beyond 16 Bar to provide a sufficient service for all occupants. Many standard valves will not be able to withstand pressure this high, meaning non-standard, high performance valves may be required, these are often not readily available in the UK and can be subject to long lead times – causing issues when a replacement is needed urgently. 

With good planning and careful consideration, the issues surrounding excessive pressure are usually relatively easy to resolve through the use of high-pressure products and Pressure Reducing Valves (PRVs) in the system. 

PRVs are designed to restrict pressure; as water moves from the inlet port, it must pass through a spring and a diaphragm which will cause resistance and therefore lower the pressure to the desired level as the water leaves the valve through the outlet port. 

The advantage of a pressure reducing valve is that they are set to regulate the water flow to a specific pressure. That means if there is a sudden spike in pressure, the spring and diaphragm in the valve will tighten, thus maintaining a consistent and safe water supply pressure, protecting the equipment throughout the system.

It is essential that PRVs are installed in high rise buildings to assist with maintaining this consistent water pressure, due to the height of the buildings, and the need to supplement the municipal water supply to create good water pressure on the higher floors. Without the introduction of PRVs this could cause severe issues on the lower floors with regards to over pressure and water delivery. 

Systems may also experience issues if the municipal water supply is cut off or if the pressure boosting systems fail; whilst this will be infrequent, it is important to protect the system from back flow should this situation occur. The system can be protected through the use of non-return valves; these valves will prevent the force of gravity from taking the water back downstream and potentially causing damage to the pumps and other equipment.

PRVs are usually used on the legs coming off the main riser, only reducing the pressure when the water has reached the desired level. This means that the core section of the system - the riser and plant rooms - are subjected to much higher pressures and therefore valves installed within these sections must be able to withstand a much higher-pressure level. This applies to all types of valves on the core sections, such as, isolation, commissioning, check and strainers. These valves are essential for the smooth operation of the system and to enable maintenance to take place; it is of paramount importance that the right pressure rated valves are used to prevent leaks and damage to the system.

Whilst the aim of a PRV installation is to reduce the pressure at the relevant level, this can also happen unintentionally if proper precautions are not put in place. Debris in pipework can clog the pipes and therefore reduce the flow as it passes, which could cause circulation and water pressure issues for the occupants. Strainers can lessen the chances of pipework becoming clogged by capturing any debris as it attempts to pass the valve, not allowing it to make its way further into the system. 

Isolation valves are another example of a valve that would need to be installed throughout a system, including on the pipework that is running at a high pressure. Isolation valves are an essential part of every system, allowing engineers to isolate a section of the system to carry out routine maintenance and emergency repairs throughout the lifetime of the system. 

Albion’s PN25 range includes butterfly valves, non-return valves, strainers, a double regulating valve and an orifice plate. 

19 August 2020

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