But the issue can often be addressed with Pulsation Dampeners.
The Pulsation Dampeners, usually incorporating a tubular diaphragm that separates process liquid from a gas cushion, guard against fluctuations in pressure and flow by:
- absorbing pressure pulsations in the piping,
- reducing high liquid accelerations and inertial forces in suction and discharge lines,
- avoiding excessive pressure loss and damaging water hammer,
- and, protecting the chemical feed system and metering pumps from damage.
They can also include a charging valve, pressure gauge, system connections, and mounting bracket, and should be made from corrosion-resistant materials. (The related housing should be made from PVC or polypropylene, with the elastomeric diaphragm and seals generally made from Hypalon®, Viton®, or EPDM.)
Consider why they’re needed
The intermittent flow patterns generated by a metering pump can cause instantaneous liquid velocities that are three to five times higher than 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 the pressure pulsations and creating a continuous flow – helping to reduce the wear and tear on system components including the pump. It can also reduce problems in systems that have under-sized piping or long piping runs. These components can be installed on the suction side of a pump, improving the Net Positive Suction Head (available).
How they work
The space between a Pulsation Dampener’s diaphragm and housing is charged with compressed air or nitrogen gas to approximately 60 per cent 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 by perforations in the support pipe. This liquid contacts the diaphragm and compresses the gas cushion, storing a portion of the liquid. As the flow from the pump decreases, the liquid that is stored in the Pulsation Dampener is then delivered to the system, creating a continuous flow.
Conventional installations of Pulsation Dampeners use a T fitting, requiring a dummy plug to seal off one of the connections. In these installations, the Pulsation Dampener should be installed as close to the pump as possible. On the discharge side, a Pulsation Dampener will create a 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.
However, it’s best to install Pulsation Dampeners in-line with the piping, to address the entire volume from each pump stroke. The size of a Pulsation Dampener should be based on pump volume per stroke, and the level of dampening that’s required. In most cases, it is sufficient to dampen the pulsations to approximately 10 per cent of the average system pressure.
To determine the pump’s “volume per stroke”, divide the Pump Flow Rate (in gallons per hour) by the Pump Speed (measured by strokes per minute), and multiply that figure by 3.85. The result represents the Pump Volume per Stroke (measured in cubic inches per stroke).
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 as well.
Such a device will be required to store the liquid in the Pulsation Dampener if short discharge lines or atmospheric discharge cause insufficient back pressure.