HVAC523 Circulator Pumps

Pump mounting Most circulators are designed to be installed with their shafts in a horizontal position. The direction of flow is usually indicated by an arrow stamped on the volute.

Pump mounting The weight of large circulator should not be supported by the system piping. If pipe support is needed, some sort of vibration-absorbing materials needs to be used.

Pump mounting

Pump mounting A common practice with a multiple zoned system is to install several circulators on one supply header. The far side of this header should be well supported to prevent it from bending or sagging due to the weight.

Pump mounting

Connecting the circulator to the piping Unlike fittings and valves, circulators should be mounted so that they can be removed for servicing. The usual method of connecting a circulator to piping is with bolted flanges.

Connecting the circulator to the piping Standard flanges Isolation flanges

Connecting the circulator to the piping Pump flanges are available in cast iron for closed loop systems as well as bronze or brass for open loop systems. As the flange is bolted together, an O-ring or rubber gasket is compressed between the faces of the flanges to make a seal.

Connecting the circulator to the piping A special type of flange, known as an isolation flange, contains a built in ball valve that is used to isolate the circulator from the system for servicing without having to drain the systems fluid. Only a small amount of fluid in the volute will be lost from system.

Circulator with isolation flanges

Connecting the circulator to the piping If isolation flanges are not used, it is recommended that ball valves be installed on either side of the circulator for isolation. It is highly recommended that every circulator installed on a hydronic system be equipped with one of these means of isolation.

Circulator with ball valve isolation

Placement of the circulator within the system Always install the circulator so that its inlet is close to the connection point of the systems expansion tank. Always provide a straight length of pipe of at least 12 pipe diameters long between the point of no pressure change and the inlet of the circulator. Example: ¾” copper m pipe= .75 x 12 = 9”

Why we pump away To understand why this rule should always be followed, you need to understand the interaction between the circulator and expansion tank. In a closed loop piping system, the amount of fluid, including that in the expansion tank is fixed. It does not change whether the circulator is on or off.

Why we pump away A portion of the expansion tank contains a captive volume of air. The only way to change the pressure of this air is to either push more fluid into the tank to compress the air, or to remove fluid from the tank to expand the air.

Why we pump away This fluid would have to come from or go to some other location within the system. However, since the fluid is incompressible, and the amount of fluid is fixed, this cannot happen regardless of whether the circulator is on or off.

Why we pump away The expansion tank thus fixes the pressure of the systems fluid at it’s point of attachment to the piping. This is called the point of no pressure change within the system.

Pump performance Mechanical energy produced by the pump is called head. A definition of head (In a hydronic system) is the height to which a pump can lift and maintain a column of water.

Taco pump curve chart

Pump head We use the term "Pump Head" to describe the force the circulator develops to overcome pressure drop. When we work with closed hot water heating systems, "Pump Head" has nothing to do with the height of the building. Height, as far as the circulator is concerned, doesn’t exist.

Pump head It has only to do with the circulator’s ability to overcome friction. That’s because the system is completely filled with water. The circulator doesn’t know (or care!) if the building is 100 feet high and ten feet wide, or ten feet high and 100 feet wide. All it knows is friction.

Pump head Pump Head has a lot to do with the number of fittings or valves and the size of the building’s piping network. But it has nothing to do with gravity or the fill pressure of the system.

Circulators in series Occasionally, a system requires more head than can be supplied by a single circulator. When two identical circulators are connected in series, the resulting pump curve can be found by doubling the head produced by a single circulator at each flow rate.

Circulators in series

Circulators in parallel This arrangement is useful when a relatively high flow rate is required at a modest head. The pump curve for two identical circulators connected in parallel is obtained by doubling the flow rate of a single circulator at each head value.

Variable speed circulators Variable speed circulators are relatively new to North America but have been in use in Europe for many years. The pump curve can vary over a wide range.

Variable speed circulators

Variable speed circulators One excellent application for the variable speed circulator is as a constant pressure circulator. Systems having several independently controlled zone valves are good candidates for this concept.

Circulators with integral flow checks Without flow checks installed in each zone circuit, some of the flow from a separate circuit can be reversed through circulators that are off. Flow check must always be installed in each piping circuit anytime multiple pumps are installed in parallel.

Circulators with integral flow checks Some manufacturer's are offering circulator pumps with integral flow check valves. The integral flow check consists of a small spring loaded valve housed within the inlet or outlet of the circulators volute.

Circulators with integral flow checks