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Pump it Up! Why Bladder Pumps are Not as Confusing or Difficult to Operate as You Might Think

Posted on November 23rd, 2021

Low Flow Sampling Setup

Pneumatic bladder pumps are an alternative to regular submersible pumps when purging/sampling a monitoring well via low flow methodology. Bladder pumps minimize ground water sample agitation, aeration, and turbidity to achieve more accurate parameter stabilization compared to the continuous flow generated by a submersible electric pump.

These pumps operate using timed ON(refill)/OFF(discharge) cycles of compressed air that squeeze a flexible bladder to displace water out of the pump to the surface. First, fluid enters and fills the pump through a fluid inlet check valve via hydrostatic pressure. Once filled with fluid, compressed air enters the space between the bladder and the interior of the pump housing, squeezes the bladder, and pushes the fluid to the surface. The check valves ensure that no water flows back down through the pump or into the formation. The refill/discharge cycles are repeated, providing a steady flow of water up the sample line while minimizing volatilization of the sample.

The most unique aspect of utilizing a bladder pump when groundwater sampling is setting the proper discharge and refill rates in conjunction with the compressed air pressure. Operators must take into account the pump size, pump depth and submergence in water, and the controller/compressor being used in order to maintain a flow rate between 100 mL/min and 500 mL/min.

An easy way to verify that the pump is working is to submerge the pump’s discharge tubing in a bucket of water and start the pump cycle while the pump is out of the water. Each time the pump discharges, air will be expelled from the end of the discharge tubing and can be observed as bubbles in the water. To optimize the pumping rate, the discharge time should be set long enough to ensure that the air has stopped bubbling out of the tube before the pump controller switches back into refill, and the refill time should be set long enough to achieve the maximum volume of air bubbles on each pump cycle. Experimenting with different configurations of refill and discharge values can allow an operator to get a feel for what works best for their wells; not all wells screened in the same formation will pump the same way.

Several major pump manufacturers offer bladder pumps to suit any particular needs a site may have, be it a pump that can fit in a 0.75-inch PVC monitoring well, dedicated pumps for long-term monitoring, or special PFAS-free construction. Most bladder pumps use disposable and replaceable bladders available in regular polyethylene or Teflon-lined options. Air and water tubing come in several different sizes depending on what the individual bladder pumps can accommodate, as well as bonded tubing which attaches the air and water tubing together (so they do not need to be purchased separately and add ease to pump deployment and removal). Similar to the bladder, water tubing is also available as polyethylene or Teflon-lined. HDPE tubing is also available for PFAS sampling.

If you have a site that is already outfitted with bladder pumps for groundwater sampling or are otherwise in need of low-flow sampling in order to collect defensible samples per your site’s Quality Assurance Project Plan, do not hesitate to give us a call at (908) 218-0066 or email consult@jmsorge.com. We employ managers and field staff knowledgeable in the operation and application of bladder pumps and other low-flow purging equipment.

Jonathan Wood
Project Scientist

 

Further reading on low-flow purging and different equipment options include:

NJDEP Field Sampling Procedures Manual, August 2005

QEDenv.com

Geotechenv.com

Solinst.com

In-Situ.com


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