Positive Displacement Pumps and Pulsation Dampers
(a) Pulsation Damper Operation:
Positive displacement pumps, due to their internal mechanics, can generate a pulsating flow. This means the flow rate is not constant but varies with each cycle of the pump’s internal element (gear, vane, piston, etc.). A pulsation damper, installed on the discharge line, helps mitigate these pulsations. Here’s how it works:
- Components: A pulsation damper typically consists of a housing containing two chambers separated by a flexible bladder or diaphragm. One chamber is pre-charged with an inert gas (like nitrogen) and connected to the gas side of the bladder. The other chamber connects to the pump’s discharge line and fills with fluid.
- Energy Absorption During High Flow: During the high-flow phase of the pump cycle, the pulsating pressure in the fluid chamber pushes against the bladder, compressing the gas in the gas chamber. The compressed gas acts like a spring, absorbing the excess pressure and energy from the pulsating flow.
- Energy Release During Low Flow: During the low-flow phase of the pump cycle, the compressed gas in the gas chamber expands. This pushes the bladder back, forcing fluid back into the discharge line and smoothing out the pulsations in the flow rate.
(b) Why Some Positive Displacement Pumps Don’t Need Pulsation Dampers:
Not all positive displacement pumps require pulsation dampers. Here’s why some types can operate without them:
- Internal Design: Certain pump designs inherently produce minimal flow pulsations. For example, some multi-vane pumps with a high number of vanes or screw pumps with overlapping helical rotors create a more continuous flow compared to pumps with fewer vanes or pistons.
- Operating Speed: Lower operating speeds generally result in less pronounced flow pulsations. If a pump operates at a relatively slow speed and the system pressure fluctuations are tolerable, a pulsation damper might not be necessary.
- System Characteristics: The overall system characteristics can influence the need for a pulsation damper. If the piping system has a large volume or includes components like accumulators that help dampen pressure fluctuations, the pulsations might be sufficiently mitigated without a dedicated damper.
However, factors like:
- High Operating Speed: Increased pump speed often leads to more significant flow pulsations.
- Low System Volume: Systems with limited volume have less capacity to absorb pressure variations.
- Sensitive Equipment: If the system includes pressure-sensitive equipment susceptible to pulsations, a damper might be necessary.
In conclusion: The decision to use a pulsation damper depends on the specific pump type, operating speed, system characteristics, and desired performance outcomes. When pulsations are a concern, consulting with a pump expert to determine the appropriate solution is recommended.