Design And Construction Standards For End Suction Pumps
An end suction pump complete with isolation valves, vibration isolators, a suction strainer, long-radius ell and reducer at inlet, spring-supported inertia block, drain pan, and other amenities typically associated with hydronic service is a single stage pump with only one impeller. Isolation valves, if required, are typically butterfly, gate, plug, or ball valves, depending upon line size and duty requirements. The weight of the piping to the vibration isolation fittings is typically supported by overhead suspension.
A strainer is required to collect debris in the system. The strainer includes a provision for blowdown, which will allow loose debris to be flushed from the strainer when the pump inlet valve is closed and backflow from the release of the pump by the flush valve occurs. The flush valve is typically a 2-in. diameter or larger ball valve installed complete with a piping “tail piece” routed to a floor drain for spill containment. The screen in the strainer should be specifically chosen for use in a water system. If a strainer is used in a condenser water system, it should have openings in it larger than that associated with chilled water service. Often the strainer in a cooling tower basis suffices for this purpose, and the one in the piping is not required. Since strainers can be purchased integral to air separators and pump suction diffusers, drawings and specifications should be carefully coordinated to ensure that only one strainer is installed in a chilled or hot water hydronic system.
An end suction pump requires either a straight length of pipe into the pump suction or a suction diffuser. If a straight pipe section feeds the pump, the straight pipe section should be at the minimum three pipe diameters long, be fed via a long radius elbow, and incorporate a reducer fitting at the pump inlet. All of these promote uniform flow into the pump impeller. Depending upon the weight associated with the pump inlet piping from the vibration isolator downward, a stanchion pipe sustain may be required. If it is required and no spring-secluded inertia pad is used, the stanchion should be supported from the pump base. typically, with small pumps, a spring-isolation inertia pad is not required.
It is shared practice and necessary in hydronic systems to use an increaser at the pump outlet. This is because of a noise consideration associated with high-velocity flow at pump release. A check valve is required in a pump release when pumps are in similar or when water must be retained in a system to keep it complete, such as for a cooling tower mounted at rooftop level above a mechanical equipment room.
Provisions should be made with all pumps for measuring differential pressures so that pump flow can be determined from the manufacturer’s pump curves. The arrangement allows a single gauge to be used for pressure measurements. The use of Pete’s plugs is suggested in situations where pressures are not excessive (