Consider why they are needed

Metering pumps are reciprocating mechanisms that produce intermittent / non-continuous flow patterns, which cause pressure pulsations. This type of flow pattern causes instantaneous liquid velocities exceeding 3-5 times the velocities of continuous flow. The intermittent flow also causes high liquid accelerations and inertial forces that can result in excessive pressure losses and damaging water hammer. A properly sized Pulsation Dampener can alleviate these conditions by dampening out the pressure pulsations and creating a more continuous flow.

Pulsation Dampeners are used to reduce wear and tear on all system components, including the pump. They also reduce problems in systems that have under-sized piping or long piping runs. A Pulsation Dampener can be installed on the suction side of a pump, thus improving NPSHA conditions. Pulsation Dampeners are needed in applications that require the accuracy of a metering pump, but cannot tolerate intermittent flow, such as filling, mixing and spraying applications.

How they work

The space between the diaphragm and the housing is charged with compressed air or nitrogen gas to approximately 60% of the expected system pressure. This gas cushion is compressed when exposed to each pump stroke. As process liquid enters the Pulsation Dampener, the liquid is distributed via perforations in the support pipe. This liquid contacts the diaphragm and compresses the gas cushion, thereby storing a portion of the liquid. As the flow from the pump decreases, the liquid that is stored in the PDS is then delivered to the system, creating a more continuous flow.

Some Pulsation Dampeners are unique in their design, in that they can be installed in-line with the piping. This installation is most effective, because the entire volume from each pump stroke passes through the Pulsation Dampener. It is also possible to install Pulsation Dampeners in a more conventional way by using a ‘T’ fitting. If a ‘T’ installation is chosen, a dummy plug must be used to seal off one connection. The Pulsation Dampener should be installed as close to the pump as possible. On the discharge side, a Pulsation Dampener will create continuous flow from the Dampener to the injection point. On the suction side, a Pulsation Dampener will create continuous flow from the chemical supply tank to the Dampener.

Sizing the Pulsation Dampener

Pulsation Dampener sizing is based on pump volume per stroke and the level of dampening required. In most cases, it is sufficient to dampen the pulsations to approximately 10% of the average system pressure. To determine the pump “volume per stroke” the following formula can be used:

A / B x 3.85 = C, with A representing the Pump Flow Rate (Gallons per Hour), B representing the Pump Speed (Strokes per Minute), and C representing the Pump Volume per Stroke (Cubic Inches per Stroke).

Dampening for Flow Meters

If a Pulsation Dampener is used to ensure constant flow for a flow meter, it might be necessary to install an orifice plate or a throttling valve after the Pulsation Dampener. In cases where short discharge lines or atmospheric discharge result in insufficient back pressure, such a device is required to store the liquid smoothly in the pulsation dampener.