What are the differences between a single and double suction pump and what advantages does one have over the other? That’s what we are exploring this week. The central difference between a single and double suction pump is the latter has an impeller designed to....
As a result, double suction pumps are also less vulnerable to the wear and tear caused by axial thrust, which occurs when water enters the impeller. Since water enters both sides of a double suction impeller, one side effectively cancels out the axial thrust of the other – assuming that flow is even on both sides. But since that is not always the case, double suction pumps have inboard and outboard bearings to absorb some of this load. These bearings can afford to be smaller than those on single suction pumps simply because there is better balance across the shaft of a double suction pump.
We typically recommend a double suction pump design for HVAC applications around 2,000 GPM or an 8” pump size. When it comes to applying a double suction pump we suggest:
(1) Selecting a pump with the shortest shaft span possible to minimize shaft deflections.
(2) Specifying based-mounted pumps with flexible couplers whenever possible. These pumps are easier to service than double suction inline pumps, which require the motor to be removed to periodically replace worn out throttle bushings.
Generally speaking, a double suction pump can be twice the cost of a comparable single suction design. Obviously, pricing is positive when it comes to single suction pumps. They are also easier and less expensive to maintain. On the other hand, double suction pumps last longer – as much as 30 years. The double suction design eliminates the axial forces on the impeller which allows for higher flows than single suction.
When it comes to selecting a double suction pump, there are three types to choose from, including:
Horizontal Split Case – These pumps have a “clam shell” type volute that is split horizontally across. The top part of the volute is bolted to the bottom. It has been around for close to 100 years. Because the pump is split horizontally, there is significantly more service time and rigging required to lift the heavy top of the pump. Watch for very old specifications. Many people called double suction pumps “split case,” all of these pumps have split casings. It just depends on whether the case is split horizontally or vertically.