Grooved systems optimise efficiency

Grooved-end mechanical piping systems reduce the mechanical room footprint, enhance system performance and save time and cost on installation, says Kris Holvoet, Product Engineer at Victaulic.

Controlling costs and compressing schedules without sacrificing quality are key concerns for contractors responsible for mechanical room installations. Clients are looking for on-time, on-budget delivery of high quality systems that work well and are easy to maintain.

Alongside these drivers, space is becoming a critical factor. The high cost of commercial and industrial building space and its scarcity has led to a growing trend to squeeze the size of mechanical rooms. Ever tighter architectural designs for new builds are putting pressure on consulting engineers and contractors to deliver reliable, cost effective HVAC solutions that keep the mechanical room footprint to a minimum. Similar demands are being made for mechanical room retrofits within the structural constraints of older buildings.

Grooved-end mechanical piping systems address all of these issues.  The lighter weight, smaller size yet higher integral strength of grooved components compared with welded or flanged systems, make them ideal for projects that are tight on space or where mechanical rooms are located on higher level floors. Their ease and speed of installation offer savings on total installed costs and they also deliver improved performance and reliability.

Eliminating rubber bellows

Grooved couplings are designed with an elastomeric gasket contained inside the internal cavity of a ductile iron or stainless steel housing and secured by two nuts and bolts to create a leak-tight joint. This unique design gives the couplings noise and vibration reducing properties superior to those of traditional devices.

In traditional mechanical room set-ups rubber bellows or compensators are placed in the piping system at either side of the pump to reduce noise and vibration and are sometimes used to correct misalignment between welded pipe and equipment, placing the rubber under intense stress in a certain plane.

Not only do they take up valuable plant room space, but rubber bellows are considered the weakest point of an installation and the first component that is likely to fail, as general wear and tear, along with exposure to UV light in the mechanical room, causes the rubber to erode. They also require on-going maintenance as bolts gradually slacken and the system starts to weep, the bolts need to be tightened regularly. With a best life expectancy of 10 years, rubber bellows may need to be replaced several times within the life of the system which involves system downtime plus the cost of a new unit. Failure of the rubber bellows can be sudden and unpredictable, causing serious health and safety risks if, for example, the rubber splits and water escapes.

Installing three grooved flexible couplings on each side of a pump solves these problems. It eliminates the need for costly, bulky flanged units and avoids the use of rubber bellows. The coupling construction enables the gasket to seal against the pipe, while the metal housing provides both space for the resilient elastomeric material to flex, and containment to prevent overstretching. This creates a discontinuity similar to that of a rubber compensator. Additionally, ductile iron and stainless steel both have their own vibration dampening qualities, so the external housing also serves to absorb sound, thereby protecting equipment and enhancing the life time of the system.

A further advantage is removing the need for tie rods or the type of bracketry required to support pipework on top of and beneath bellows which increases time, labour and material costs. Special bracketry must either be prefabricated or fabricated on site and can account for around two thirds of the cost of installing a metre of pipe. Installations with flexible grooved couplings avoid these issues as they only require conventional brackets.

Three flexible couplings can be used not only with pumps but also with chiller units, cooling towers and any equipment with an engine that causes vibration. The use of additional grooved couplings in the distribution lines will further reduce the transmission of vibration. By combining versatility with durability, the method provides a low maintenance solution that saves space and delivers both practical and commercial benefits throughout the life of the system.

In addition to noise and vibration attenuation, grooved couplings allow for alignment ease in a pump installation. The pipe and system components can be fully rotated before tightening, without creating stress on the pump flange or equipment connection. Flexible couplings also help to accommodate slight deviation that might be caused if pipework has not been prefabricated to exact dimensions – something which is more difficult to achieve with a welded or flanged system.

Improving pump efficiency

Cavitation is a problem frequently experienced, especially where space is limited.

When turbulent water enters a pump chamber and the suction eye of a pump impeller, the degree of turbulence has a direct correlation with lower pump efficiency and greater hydraulic noise within the pump casing. To reduce the effects of turbulence before the water enters the centrifugal action of the pump impeller, suction pipes are typically kept as long and straight as possible before the connection onto the pump flange. Yet creating long lengths of pipe does not sit well with modern design trends which aim to keep mechanical rooms simple and compact.

Where a bend is connected directly onto the pump suction, the water flow may spin in opposite directions within the eye of the impeller. Pump energy then has to be spent correcting this action before producing the expected performance. Inevitably, both flow and pressure measurements will be less than those expected at the design stage. A simple alternative is to fit a type of strainer called a suction diffuser which straightens out the spinning fluid created by the change in direction (bend) and enables pipework to be connected closer to the pump at a 90 degree angle. Eliminating long pipe runs, elbows and reducers makes for a smaller mechanical room footprint and optimum pump performance.

Designing mechanical rooms with grooved valves achieves similar space savings. Traditionally, check valves and butterfly valves need a spool piece between them to avoid damage to the valves. Having grooved check valves, close-coupled to grooved butterfly valves, eliminates the use of flanged spool pieces on the pump dressings and cuts out the need for flange adapters.

Cutting labour risk

Driving down costs is a key objective for contractors. Whilst material costs are relatively easy to fix, labour costs are more volatile, leaving contractors open to significant risk on project costings. The grooved mechanical system reduces that risk by a large factor and competes favourably on total installed costs because a larger proportion of the total costs is fixed. When other joining methods are used, typically 70% of costs are subject to variation making it difficult to estimate, which means a greater risk to the project budget. A grooved mechanical system with a quick and simple joining method and no need for jobsite preparation offers considerable cost saving opportunities on installation.

Switching from welded and flanged specifications to the grooved method for mechanical room installations can make a big difference to the success of a project and its use is becoming more widespread. Because manufacturers of pumps and some other types of equipment have come to realise the advantages of grooved technology, many now offer a grooved outlet as a standard option. Not only does it make for easier product testing in the factory, but manufacturers know that having a grooved conne
ction reduces the likelihood of additional forces on the equipment that could damage it.

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