The 700 bar XVARI XA air-over-hydraulic pump from Enerpac (A Division of Actuant Corp) features high oil flow, with its rotating air motor and rotating two-stage pump element, giving hydraulic delivery up to 50% higher than conventional pumps with linear motor and single piston.
Tony Cooper, one of the engineers who contributed to the pump’s design, traces the evolution of the pump and the reasons for the change it delivers. In the late 1950s, Enerpac (then Blackhawk) introduced the first air-over-hydraulic pump, which was primarily used in automotive collision repair markets, but which became popular in other industries too because of its versatility. Their use has spread to industries such as manufacturing, mining, machinery maintenance, electrical component production and testing and forming applications in industries as diverse as construction and primary production.
Air-over-hydraulic pump technology makes use of a reciprocating linear air motor that drives a single piston hydraulic pump. While this original proven design continues to meet the needs of many markets, others have a longstanding and, until recently, unfulfilled wish for advanced hydraulic functions.
After conducting an extensive series of end-user interviews around the globe, Enerpac decided to start the development of an optimum pump design with a clean sheet of paper. End-users in all target markets provided crucial input that resulted in a comprehensive list of design guidelines. After mapping out all of the Voice of Clients (VOC) data, the Enerpac development team realised that the customer expectations for a new small air driven hydraulic pump could not be satisfied with the old reciprocating linear air motor technology.
A clear sign was given by the VOC data that the market was ready to accept more hydraulic horsepower, leading to higher productivity, as well as preferring variable speed and fine metering to provide more control and safety to the end-user. High on the wish list was also the desire for ergonomic improvements: end-users wanted a product that allowed them to keep both feet on the ground while operating the pump. They also wanted a stable product that did not have the tendency to tip over - and a pump less prone to contamination.
The result of the market preference for higher hydraulic delivery was the XVARI XA series’ hydraulic delivery being up to 50% higher than with conventional air-over-hydraulic pumps. The Enerpac development team achieved this by using a rotating air motor and a two-stage rotating pump element instead of a linear air motor.
The pump element is driven by an eccentric shaft with cams for the separate drive of a low-pressure piston and a high-pressure piston. The cams are 180° phased to eliminate vibration.
A planetary gearwheel mechanism has been placed between the air motor and the pump element to reduce the speed of the air motor (20,000 rpm) to the 2000 rpm that the hydraulic pump runs. Due to higher piston speeds, this configuration results in a smoother hydraulic flow as opposed to the pulsating hydraulic flow of the reciprocating linear pump technology. Since this new technology is entirely different from the linear air motor technology, the term of air-over-hydraulic pump properly does not apply to XA-series.
The advantage of the rotating air motor is that the speed can be accurately controlled by means of a throttle valve. By pressing the pedal further down, more air goes to the motor and the speed increases. This provides for a variable oil flow, so that the speed and positioning of the hydraulic cylinder or tool can be controlled precisely. The user has now more control over the hydraulic application, resulting in better quality and safety.
For the pressure release function – also important to many industry sectors - the Enerpac development team invented a high-pressure metering valve with variable oil flow that allows the operator for precise load lowering. This valve is accurately controlled by the release pedal. The more the pedal is depressed, the faster the cylinder retracts and the pressure reduces. This results in better control over the retract function; for example, a load that must be lowered slowly and in a controlled manner.
In applications where controlled cylinder retraction is not required, the pedal can be fully depressed and the cylinder retract speed exceeds that of conventional air-over-hydraulic pumps.
The XVARI XA series makes use of a collapsible rubber oil reservoir (bladder), making the pump less vulnerable for contamination from the outside. In this way, no air venting screws or openings to the outside are required, making the XVARI XA series pump a fully closed hydraulic system. As a result, the pump can be used in horizontal and vertical positions and no dirt or debris can enter.
The unit is provided with a foot-operated release lock that saves time when using slow-retracting actuators. For transportation, the pump is provided with an integrated (self-retracting) carrying handle.
Safety is a keynote of the design. The footprint of the XVARI XA series is slightly larger than that of most conventional pumps, but the unit is lower, more stable and cannot turn over.
The XVARI XA series development team spent extensive time to better understand workplace conditions and human posture in an effort to minimise forces acting on the human body. The objective was to reduce unnecessary muscular force, while maintaining full control of the pump actuators when operating the pump. Several concepts of pump actuation were prototyped and tried out with intensive consultation of everyday users.
In the final analysis, allowing the operator to rest his weight on both legs improves the stability and balance of the human body, reducing fatigue in trunk and upper limbs.
From testing the various models, the team decided for having two pedals; one for the pressure build-up (tool advance) and one for pressure reduction (release or tool retract). This two-pedal model meets the objective of an ergonomically better product. The pedals are depressed with the ball of the foot, whereby the heel stays on the ground. The body weight therefore rests on two legs during the operation. This causes less fatigue and provides an increased stability and also a better control over the degree of pressing and control of the pump.
To control the pressure, the pump can be optionally equipped with an integrated pressure gauge. The completely closed housing is manufactured from durable glass-filled nylon and provided with an extra protection on the corners in the form of stiff cast rubber corner pieces. Throughout the course of its evolution, the new Xvari XA pump was continuously tested against the needs of the market.
After prototyping and extensive lab testing, the XVARI XA series pump development involved two rounds of field testing to validate the design in terms of hydraulic performance, ergonomics and functionality. Working with a global team of Enerpac field test champions, prototypes were field-tested on sites comprising of all target markets. Field tests were conducted in Europe, USA and Asia Pacific region.
End-user input was gathered and statistically appraised. On the basis of these inputs, the product concept was further optimised and subsequently tested in a second round of field tests around the globe. The XVARI XA series pumps offer advantages like high oil flow, precise control and ergonomic operation combined in one hydraulic pump.