The Pump Wizard    |    Submersible Pump Overview    |    Feature Comparison Table    |    Cost Comparison Chart Home > Pump Overview > Piston Piston pumps have been used traditionally for applications as diverse as farmhouse windmills and oil wells. In the recent era they have been adapted for use at ground water remediation and landfill sites, which can benefit from the ability of piston pumps to handle high temperatures, viscous fluids, solvents, explosion hazards, depths to 400 ft. and corrosive liquids. Slant or horizontal wells can also be pumped with piston pumps. They are available with air or electric powered reciprocating drive units located at the wellhead. A drive rod connects the drive unit with the piston, which reciprocates in the pump cylinder down in the well. Image: Piston pump elements Down-well piston pumps all function basically the same: a piston with a check valve is raised and lowered in the pump cylinder located down in the well, lifting fluid above the piston toward the surface and drawing more liquid from the well into the pump cylinder from below.  On the lift stroke, the liquid above the piston is raised toward the wellhead. Each lift stroke also applies suction to the pump cylinder below the piston, drawing more liquid into the pump through a second check valve at the bottom of the cylinder. On the piston down-stroke the piston does no work as the liquid just passes through the piston's check valve as the piston heads downward. The piston/cylinder design and the drive unit are the key components to consider in evaluating piston pumps for remediation and landfill sites. The piston/cylinder design used in oil well piston pump technology is most relevant to difficult pumping applications, because this technology has been refined for over a century to provide long service life in challenging conditions of high temperatures and viscosities, solids and corrosives. Oil field pistons use hardened metal surfaces and an extremely close piston to cylinder fit to provide a durable liquid seal and avoid damage from abrasive solid particles. In contrast, piston pumps for water and other mild applications use elastomeric seals on the piston, but these tend to be damaged quickly and have a short service life if solids or solvents are present. However, even with oil field type stainless steel pistons and cylinders, abrasive solids will still cause faster wear on piston pumps than on air-powered automatic pumps. The drive unit for a piston pump can be powered by compressed air or electricity. Air power has advantages in system simplicity, explosion hazard, speed control, "soft" failure modes, serviceability, flow rate, level control and cost. With air power, the drive cylinder simply stalls if the piston or discharge flow meet unexpected resistance, without damage occurring. Simple adjustments to the air flow allow the liquid flow to be adjusted. The same compressed air supply that drives the pump can be used to operate very durable bubbler type on/off level controls for the pump. Electric powered piston pumps have an advantage at wells already equipped with electric power, not compressed air, and some sites simply prefer electric power over compressed air systems. Electric drives are considerably more expensive than air-powered models, have more restricted operating limits of ambient temperature and humidity, lower maximum flow rates and are more complex to operate and service due to their sophisticated industrial control electronics. Electronic level control systems tend to require more maintenance than pneumatic bubbler tube types. The intake suction of piston pumps allows them to readily pump viscous fluids and to draw down the liquid level to lower levels than with air-powered automatic pumps and electric submersible pumps. These features are especially advantageous for removing DNAPLS and heavy crude oils. Some piston pump users see a strong advantage in the ease of service of piston pumps, because the driver is located conveniently at the wellhead, and the drive rod and piston are light weight enough to be easily lifted and removed by one person. However, servicing the pump cylinder downwell requires lifting and removing all of the threaded drop pipe it is attached to. Pumps are delivered as a complete system, except for the drop pipe to which the pump cylinder is attached; local purchase of standard pipe and couplers saves shipping costs. A two-person crew is recommended for installation of the drop pipe. Controls Controls on piston pumps include the control of the driver reciprocating motion and the pump on/off control. Air-powered drivers use either external industrial control valves and limit switches or an internal reverser mechanism built into the air cylinder. Image: Control system The internal reverser is a simpler system, protected from the weather inside the drive air cylinder. On/off control is achieved by a bubbler level sensing system or off timers adjusted through site experience. Electric powered drivers require a linear actuator, a variable speed motor control and some form of programmable logic control and sensors to provide the reciprocating drive motion. The electronic controls must be adapted to handle the site temperature and humidity conditions to avoid damage to the controls and maximize the operating range. Emulsification of Free-Phase Liquids The low speed, simple motion of piston pumps minimizes fluid shear in the pump, and therefore minimizes emulsification of any free-phase present in the pumped liquid. Less emulsification tends to improve the performance of any downstream treatment equipment, such as oil/water separators. Diameter Piston pumps are available in sizes to fit 2-, 3- and 4-inch diameter wells. For a given driver, a smaller downwell piston will pump from greater depths but at lower rates,while a larger piston will pump at higher rates but will be limited to shallower depths. Materials Manufacturers offer a range of materials of piston pump materials of construction to meet site-specific conditions. Some of these materials include stainless steel, CPVC and glass reinforced epoxy. Temperature and chemical resistance have an important influence on materials selection. Temperature Based on their oil well application history, piston pumps are well suited to high temperature applications, provided the proper materials are selected. Even electric powered models are unaffected, since the motor is outside the well. Summary of Piston Pump Strengths and Weaknesses Strengths Ability to pump from depths down to 400 ft or more Ability to pump high viscosity and high temperature fluids as well as solvents and corrosives Can pump from slant and horizontal wells Easier service accessibility of key components above ground Complete systems available from one source Does not directly introduce air contact with the pumped liquid, which can cause fouling deposits at some sites Both air-power and electric version available Very little emulsification of hydrocarbon mixtures No downwell electric hazard, even with electric powered version Weaknesses Not capable of higher flow rates of electric submersible pumps and air-powered automatic pumps Higher priced than air-powered automatic pumps and most electric submersible pumps Likely to have higher long term service costs than air-powered automatic pumps, especially if high levels of abrasive solids are present Tel (734) 995-2547 • Toll-Free in North America (800) 624-2026 • Fax (734) 995-1170 © 1982 - 2004, QED Environmental Systems, Inc.   All Rights Reserved.