The deep well progressive cavity pump is a positive displacement pump that discharges a fixed amount of water per cycle. Using a spiral rotor instead of a reciprocating piston, water is extracted from depths of up to 300 meters underground. These pumps are suitable for all stages of emergency situations.
Most deep well screw pumps are mechanized, but there are also manual pump versions. They use rotation instead of reciprocating motion to work. There are different driving mechanisms that can be driven manually, electrically (grid or solar), or by diesel/gasoline engines. In the past, the drive mechanism was located on the ground and connected to the drive shaft (via a V-belt or gear transmission head), but now the electric motor is tightly coupled to a small section of flexible drive shaft inside the borehole. In both cases, the drive shaft is connected to a single helix metal rotor, which maintains continuous contact with the double helix rubber stator and rotates within it.
Design considerations
Deep well screw pumps can operate within a depth range of up to 300 meters, with a flow rate of up to 50000 liters per hour at low head. Generally speaking, they are the preferred pumps for high head and low flow requirements. They operate through the rotation of a helical rotor, which is in the form of a single helix and located within a fixed double helix rubber stator. Water occupies the cavity between the two, and when the rotor rotates, the cavity moves upward together with the water, causing the water to be lifted in the ascending main pipeline. This rotary design does not require a check valve system, while reciprocating pumps require a check valve system, but usually a bottom valve is still installed below the rotor to prevent backflow. The advantage of mechanized positive displacement pumps (with screw pumps being the main type) is that the water flow rate does not significantly change due to differences in head. Operating this type of pump requires consideration of various factors. These pumps can be set in parallel, with both pumps pumping water into the pipeline. If the driving mechanism is located on the ground and the vertical driving shaft is located in the borehole, the borehole also needs to be vertical so that the driving shaft can be suspended vertically. In addition, the pump should never be operated with the valve closed, as this may damage the pump and accessories. Screw pumps also exist as suction pumps (not just deep well pumps), in which case the maximum height at which water can rise in the pipeline depends on atmospheric pressure, which itself varies with altitude. Another design consideration for a motorized suction pump is to ensure that the suction port maintains sufficient pressure to prevent cavitation. Under low pressure, bubbles will form in water, which will then burst, triggering shock waves and causing serious damage to the pump. To prevent this situation, it is necessary to calculate the net positive suction head (NPSH) using the atmospheric pressure at the pump location, NPSH data provided by the pump manufacturer, friction losses in the inlet pipeline, and steam pressure.
Material Science
The required materials include the rising main pipe, drive shaft (stainless steel), motor, spiral rotor (usually chrome plated steel), stator (rubber), and bottom valve. This type of pump is produced and exported in a few production bases in a few countries/regions.
Applicability
Deep well screw pumps are an ideal choice in emergency situations, as detailed pumping design is often not possible in advance (in contrast, speed pumps typically require good design). This means that a pump can be used for different heads without significant changes in flow rate. Compared to other common types of drilling pumps such as speed pumps, these pumps are also more suitable for pumping water containing solid or abrasive particles and can be used for both drinking and non drinking water applications. Nevertheless, the drilling pump still needs to be accurately sized and positioned to prevent excessive speed from passing through the screen.
Operation and maintenance
Deep well screw pumps have a simple mechanical design, which makes them typically more reliable and easier to maintain than other mechanical pumps. In traditional designs, when the drive mechanism is located on the ground, everything is easily accessible, making maintenance simpler. However, the problem of continuous pump vibration often leads to shaft seal failure. The current design of submersible pumps includes tightly coupled motors and flexible shafts without joints, which means that the lifespan of the parts is five times longer than before. However, at this time, motor maintenance requires dismantling it from underground, which also involves dismantling the riser. However, the stator will wear out first, and every time the stator is replaced twice, a rotor should also be replaced. The stator in storage deteriorates faster with increasing heat, humidity, sunlight, or ozone, so it must be stored correctly. If the stator has been used for more than five years, there will be some deterioration before installation, and the service life will be shortened. The parts of this pump are made of metal; When these components come into contact with groundwater with a pH value of 6.5 or lower, corrosion is likely to occur, which means that the affected components need to be replaced more frequently. For this pump, the galvanized iron riser main pipe poses a greater risk than other metal components made of stainless steel, such as drive shafts and spiral rotors.
Health and Safety
Only trained personnel can operate mechanical pumps. The equipment should be prohibited from public use, and any fast-moving V-belts should be protected. For some metal pumps, chemical water quality may be an issue. When the pH value of groundwater is 6.5 or lower, iron in pipelines may begin to dissolve, causing indirect health risks, and lead may seep out from certain welds and fittings regardless of the pH value. If an engine driven pump is used, the potential health risks posed by engine emissions should be evaluated.
progressive cavity pump cost
The cost of a screw pump at a depth of 50 meters is approximately $1250. Typically, the lifespan of a stator ($170) is about 12000 hours, but regardless, due to the shelf life of the rubber, it should be replaced every three years. The lifespan of the rotor ($140) is approximately 30000 hours.
Social and environmental considerations
The end users of the water supply system usually do not interact with these pumps. The complexity of system O&M should be considered, as it requires well-trained and capable personnel. When using this type of pump, the risk of overdeveloping (underground) water resources should be considered. For electric pumps, the main environmental considerations are related to the use of consumables (lubricants, oils, chemicals) and power sources. Appropriate consumable control and disposal plans should be developed. Pumps can also be powered by solar energy to limit their impact on the environment during operation.