A Study of Piston Pumps

The piston pump plays a critical role in the hydraulic systems of civil aircraft where it is used to convert mechanical energy into hydraulic energy. This energy is then used to supply power to the actuators to fulfill the flight posture adjustment, retract and extend the landing gear, and brake. The most common type of piston pump in aviation is the swash plate type axial piston pump, due to its compact design and simplicity. Pumps of this type are capable of working at extremely high pressures while maintaining high overall efficiency.

The primary needs of fluid power systems within modern civil aircraft are high pressure, high power, integration, and intelligent control. Required characteristics of civil aircraft, including reliability, safety, and a long service life, also present technical requirements of the pump. Aviation piston pumps, unlike industrial pumps, encounter challenges including cavitation caused by low inlet pressure, large pulsation and noise, and tipping of rotating components. These factors can reduce the volumetric efficiency of a pump and increase fatigue wear, shortening the life of the pump. Furthermore, the compact design of hydraulic systems weaken heat dissipation, sometimes leading to rapid temperature increase and functional failure.

Aircraft pumps can be divided into two categories: fixed displacement and variable displacement. Fixed displacement pumps provide flow that is directly proportional to the speed of rotation, that ratio being the displacement of the pump expressed in volume per revolution. Variable displacement pumps, as their name suggests, are able to vary their displacements in response to a control mechanism. Fixed displacement pumps are more common due to their smaller and less complex design. They are used in applications such as electro-hydrostatic actuators (EHA), braking systems, and steering systems. Variable displacement pumps are commonly used in central hydraulic systems where pump output is controlled by factors other than pump speed.

The piston pump, in its most basic form, dates back to the 16th century when it was developed to draw water in mines. Nevertheless, it was not until 1905 when the first valve plate type hydraulic pump was developed for the steering system in naval vessels. This introduced mineral oil as the transmission medium and served as the prelude to modern hydraulics. The technology continued to develop and piston pumps began being used in civil aircraft after World War II. Following this, special designs had to be developed to adapt to the harsh conditions and high altitudes. Since that time, countless design improvements have been developed to benefit the efficiency, reliability, and maintainability of pumps.

The most significant design features of a piston pump are the centrifugal boost impeller, attenuation, electrical depressurization valve, blocking valve, gerotor, and the rotating mechanical seal. The impeller ensures that the piston’s bores fill properly, and the attenuator minimizes outlet pressure pulsations within the aircraft’s hydraulic system. The electrical depressurization valve (EDV) ports outlet pressure to a depressurizing position, therefore lowering the pressure at which leakage is circulated. The blocking valve is used to allow sufficient decompression of the outlet fluid of the system before the valve closes. The gerotor ensures case drain flow against the maximum back pressure of the system, thereby decreasing the operating temperature and lowering the pressure on the pump. Finally, the rotating mechanical seal ensures fluid remains sealed in high speed cases.

At Fulfillment 3Sixty, owned and operated by ASAP Semiconductor, we can help you find all types of piston pumps in addition to a broad range of parts for the aerospace, civil aviation, defense, electronics, and IT hardware industries. We’re always available and ready to help you find all the parts and equipment you need, 24/7-365. For a quick and competitive quote, email us at sales@fulfillment3sixty.com or call us at +1-714-705-4780.