Bladder Pumps

Bladder pumps consist of a flexible, squeezable bladder encased in a rigid outer casing. They are low-flow pneumatic devices used for sampling applications. Bladder pumps are available in a range of sizes, materials, and capabilities. This includes including models for deep wells, narrow or obstructed casings, and small-volume pumps for low-yield wells. When low-flow pumping rates are used, these pumps consistently collect high quality, uniform samples. Bladder pumps are EPA-accepted for low-flow sampling. To function, bladder pumps are lowered into a well's water column. Water is drawn into the bladder via hydrostatic pressure and is passed through a check valve at the bottom of the pump. When the bladder fills up, the check valve closes so that there is no backflow. The water is then pumped up to the surface via injected gas pressure that squeezes the bladder. A pneumatic control box on the surface usually regulates the gas pressure. The bladder pumps’ lift capabilities are directly related to the pressure rating of the bladder, the size of the tubing, the power rating of the pressure source (e.g., air compressor or compressed gas), and controller box’s ability to apply sufficient force of gas at depth. Once the bladder is empty, the gas pressure relaxed and the check valve opens again, restarting the process. This sampling process is not very intrusive within the well system, and is thereby capable of collecting very low turbidity samples (< 5 NTUs). Bladder pumps are designed to minimize the potential for sample contamination. Bladders are generally constructed of relatively inert materials, and are nonporous. The bladders’ design ensures that the injected gas does not come into contact with the sample. It also keeps the sample from contacting any of the pumps’ moving parts; thereby alleviating the danger of contamination from lubricants and fluids, such as oil or grease. Additionally, the downwell equipment is often permanently dedicated to a given well, so both samples and the well are protected from disturbance and the danger of cross-well contamination. Bladder pumps consist of a flexible, squeezable bladder encased in a rigid outer casing. They are low-flow pneumatic devices used for sampling applications. Bladder pumps are available in a range of sizes, materials, and capabilities. They include including models for deep wells, narrow or obstructed casings, small-volume pumps, and pumps for low-yield wells. Sampling pumps, groundwater sampling pumps, low volume pumps, and submersible pumps are also available. When low-flow pumping rates are used, a mechanical bladder pump consistently collects high quality, uniform samples. A bladder pump may be EPA-accepted for low-flow sampling.

To function, bladder pumps are lowered into a well's water column. Water is drawn into the bladder via hydrostatic pressure and is passed through a check valve at the bottom of the pump. When the bladder is full, the check valve closes to prevent backflow. The water is then pumped up to the surface via injected gas pressure that squeezes the bladder. A pneumatic control box on the surface regulates the gas pressure. The lift capabilities of a bladder pump are directly related to the pressure rating of the bladder, the size of the tubing, the power rating of the pressure source (e.g., air compressor or compressed gas), and controller box’s ability to apply sufficient force of gas at depth. Once the bladder is empty, the gas pressure is relaxed and the check valve opens again, restarting the process. This sampling pump is not very intrusive within the well system, and is thereby capable of collecting very low turbidity samples (< 5 NTUs).

Bladder pumps are designed to minimize the potential for sample contamination. Many low volume pump, submersible pump, and groundwater sampling pump models are available. Bladders are generally constructed of relatively inert materials, and are nonporous. The bladder design ensures that the injected gas does not come into contact with the sample. It also keeps the sample from contacting any of the pump’s moving parts. This alleviates the danger of contamination from lubricants and fluids such as oil or grease. Additionally, the downwell equipment is often permanently dedicated to a given well, so both samples and the well are protected from disturbance and the danger of cross-well contamination.

The use of bladder pumps may involve a substantial upfront investment, but by dedicating a pump to a single well, this investment can quickly be recouped. Additionally, bladder pumps are easily repaired in the field, and have few moving parts that may wear out. Although the bladder system will not be damaged if forced to run in a dry well, the bladder is susceptible to rapid pressure changes and freezing.

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