Bladder Pumps Information
Bladder pumps are low-flow pneumatic devices used mainly for fluid sampling applications. These pumps typically have low flow rates and unobtrusive design, making them ideal for collecting very low turbidity samples (<5 NTUs). They are also designed to minimize the potential for sample contamination. These characteristics are especially important for groundwater analysis, which requires representative, reproducible sampling data to obtain accurate results. Bladder pumps are EPA-accepted for low-flow sampling.
Bladder pumps are available in a range of sizes, materials, and models. These include 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.
This video provides an basic overview of bladder pumps, including their advantages, disadvantages, and operation.
Bladder Pump Operation and Composition
Bladder pumps are positive displacement pumps, which use expanding and contracting cavities to displace fluids. For more detailed information on positive displacement pumps, visit Positive Displacement Pumps on Engineering360.
Bladder pumps consist of a flexible, squeezable bladder encased in a rigid outer casing. These pumps function much like a squeeze bottle. They utilize hydrostatic pressure to draw water into the bladder and pass it through a check valve at the bottom of the pump. When the bladder is full, the check valve closes to prevent backflow, and the water is pumped up to the surface via injected gas pressure which squeezes the bladder. This gas pressure is typically regulated via a pneumatic control box. Once the bladder is empty, the gas pressure is relaxed and the check valve opens again, restarting the process.
Simple bladder pump construction. Image Credit: CLU-IN
The pump casing or housing is used to protect and contain the rest of the pump, including the bladder, valves, and pressurized gas. It is commonly made with stainless steel, which provides excellent resistance to corrosion liquids. Models made with PVC or other polymers are also available.
Bladders are generally constructed of relatively inert materials such as flexible Teflon®, 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.
Other parts incorporated in a bladder pump system include an air compressor or compressed gas canister, level indicator, and controller. The downwell equipment is often permanently dedicated to a given well, so both the collected samples and well are protected from disturbance and the danger of cross-well contamination.
Bladder pump system. Image Credit: Geopump
The lift capability of a bladder pump is 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. For bladder pump products, manufacturers will provide specifications for size, weight, and performance.
Sizing & Weight
Bladder pumps are physically rated based on length, diameter, and weight.
- Length describes how far the pump extends, usually given in inches (in or ") or centimeters (cm). This specification may include the addition of an intake screen.
- Diameter describes the size of the pump opening. Specifically, inner diameter (I.D.) depicts the empty space and outer diameter (O.D.) depicts additionally the thickness of the tubing or casing.
- Weight describes how heavy the pump is, usually given in pounds (lb) or kilograms (kg).
Bladder pump performance can be rated based on volume per cycle, flowrate, depth, and operating pressure.
- Volume per cycle (volume/cycle) describes the volume of liquid delivered by the pump from each pump cycle (filling and emptying of the bladder). It is usually given in fluid ounces (oz. or fl. oz.) or milliliters (ml).
- Maximum flowrate describes the volume of liquid delivered by the pump in a certain amount of time. The rate is usually given in gallons per minute (gpm) or liters per minute (Lpm).
- Maximum depth describes the total reach that the bladder pump has to extend down into a well for sampling or collecting. It is usually given in feet (ft or ') or meters (m).
Maximum and minimum operating pressures describe the operational pressure limits for a bladder pump. They are usually given in pounds per square inch (psi) or bar.
Selection Tip: Operating flow rate is affected by the depth or level of pump submergence. Pump performance curves are thus developed using a constant depth.