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End of time-honoured hydraulic foot pump with linear air motor is near

Hydraulic pump technology is undergoing its definitive change

A tremendously high delivery, accurately controllable and ergonomic, three characteristics of the new pump with XVARI^® Technology developed by Enerpac. Never before have these three important product characteristics been combined in one hydraulic pump. With the XVARI^® Technology, Enerpac has again set a new industrial standard for the 50-year old technology of conventional air-driven hydraulic foot pumps.

The XVARI^® Technology replaces the popular and widely-used linear air motor technology and, besides strongly improved ergonomics and a more accurate metering of the hydraulic oil flow, also offers a higher delivery and higher efficiency.

The popular air-driven foot-operated hydraulic pump is undoubtedly one of the most used industrial pumps for working with high-pressure hydraulics. We find them in such places as machine factories, production companies, mechanical workshops, maintenance companies and car repair companies. The pumps are mainly used to drive small single-acting (spring return) cylinders and other hydraulic tools. The technology was developed by Enerpac at the end of the 1950s, and Enerpac was therefore the first manufacturer to introduce hydraulic foot pumps based on this technology worldwide. In the following decennia, Enerpac and numerous competitors have admittedly brought various new generations of this type of pump on to the market. However, the technological principle has in fact remained unchanged in the past 50 years. These air-driven hydraulic pumps have an average hydraulic delivery of 0,16 litres/minute with a pressure of 700 bar. The principle is simple: the pump is driven with (workshop) compressed air from 5 to 8 bar and a linear air motor (pneumatic cylinder) in the pump operates a small hydraulic piston, with which the oil is fed from the reservoir, and the hydraulic pressure is built up. The pump unit is small and therefore has the important advantage that it is easy to move. Also, the price level of the pump unit, about €600 (depending on pump function and model) has made an important contribution to the popularity of the air-driven hydraulic foot pump.

Industry learned to live with it

Despite the advantages of mobility and ease of use, current conventional hydraulic foot pumps have a number of real limitations. For example, these pumps are fitted with an inclined pedal, and the user has to lift his foot fully to operate them. This has the ergonomic disadvantage that the whole body weight rests on one leg, which is tiring and unstable. Moreover, the small hydraulic delivery means that it takes quite a long time before the cylinder is fully extended and the maximum operating pressure is reached. For example, it takes on average more than 20 seconds to let a 10-ton cylinder with a stroke length of 152 mm fully extend and then build up to 700 bar operating pressure.

Another typical disadvantage of air/hydraulic pumps is the poor controllability. This is simply because the maximum pump delivery is reached as soon as the pedal is depressed. After all, the minimum oil delivery per pump stroke is determined by a single stroke of the linear air motor; fractions are not possible. Reversely, the oil is pressed back unhindered into the reservoir by the fast-working release valve and the spring force of the cylinder. Here also, the return flow cannot be accurately controlled. These limitations are especially important with car repair companies, for example, where accurate metering of the oil flow and thus the cylinder movement is a requirement.

Furthermore, the efficiency of the pump is fairly low, namely approx. 5 percent. Additionally, this is a physical limitation caused by the ratio between the diameter of the air piston and the hydraulic piston, as well as by the efficiency of the internal air control technology.

Finally, most conventional air/hydraulic pumps have an open oil reservoir with vent screw. This gives a risk that oil will run out of the reservoir if it tilts or falls over. The pump must therefore always be horizontal. An open oil reservoir naturally also leads to internal pollution (from dust and fluids etc.) which can cause the hydraulic system to fail. These are however technical limitations with which the industry has learned to live, partly as a result of the favourable price compared to the more expensive electric pumps.

XVARI^® Technology

To tackle these limitations optimally, Enerpac has developed a whole new technology. To obtain a perfect solution for what the market is demanding, a large number of end users in different branches worldwide were asked for their wishes and needs. As a result of these interviews, the design was based on the following three main objectives:

1. an ergonomically better product

2. an optimum controllability of the oil flow, or fine metering and

3. a higher oil flow.

Additionally, to prevent possible leakage with tilting and to prevent internal pollution, a closed oil reservoir was assumed, as well as a slightly larger base area for the stability of the pump. The development has resulted in a pump with not only a totally different appearance, but also with a totally different technology 'under the cover'.

Two pedals

The first noticeable change is that we now have two pedals: one for the pressure build-up and one for pressure reduction (release). 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 thus the control of the pump. To control the pressure, the pump can be optionally equipped with an integrated manometer.

The completely closed housing is manufactured from impact-proof plastic and provided with an extra protection on the corners in the form of stiff cast rubber corner pieces. Admittedly, the footprint is larger than that of the old pump; however, the unit is lower and thus much more stable and compact.

Under the 'cover'

Under the 'cover' of the new pump, we find a revolutionary piece of technology. Additionally, a special feature here is that existing and proven technologies and functions were used in the construction, for which patents have been applied. From the market research, it appeared that many users wanted a higher hydraulic delivery. With the new pump, the hydraulic delivery is up to about 50% higher. Enerpac has achieved this by using a rotating air motor and a two-stage rotating pump element instead of a linear air motor. The pump element has an eccentric shaft with cams for the separate drive of a low-pressure piston and a high-pressure piston. 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 2,000 rpm that the hydraulic pump runs.

The advantage of the rotating air motor is that the speed can be precisely controlled. By pressing the pedal further down, more air goes to the motor and the speed increases. This provides a variable oil flow, so that the speed and positioning of the hydraulic cylinder of the tool can be controlled much more accurately. The advantage of this is that the user has more control over the hydraulic application, resulting in better quality and more safety.

Time saving

With the higher oil delivery, the time required to get the cylinder or the tool completely up to pressure has been considerably reduced. In the first pressure build-up to a pressure of approx. 120 bar, the pump delivers approx. 2,0 litres/minute. As a result, the cylinder extends twice as fast as with conventional pumps that only deliver an average of 1,0 litres/minute at this pressure. With the following pressure build-up, the oil flow reduces gradually to approx. 0,25 litres/minute at 700 bar, which means approx. 30% more delivery than with the pumps with conventional technology. Enerpac developed a special hydraulic release valve for the retraction function. 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 product characteristic results in a much better control over the retraction function; think for example of a load that must be lowered slowly and in a controlled manner.

For the new pump, a closed rubber oil reservoir has also been used, called the 'bladder', making the pump less vulnerable. The pump can be used in both, horizontal and vertical positions and no pollution can enter.

An interesting factor regarding accuracy and safety is that the speed of the new pump is considerably higher than that of conventional pumps. With conventional pumps, a linear air motor is used and the pump speed was lower, which resulted in a pulsating oil flow that lets a cylinder advance in jerky movements. With the new XVARI^® Technology, the pump speed is much higher, so that the pressure increase and thus the advance of a cylinder is much more smoothly, which improves the operational accuracy. For example, with a hydraulic press, driven by a XVARI^® Technology pump, an operator can work much more accurately than previously. The accurate control allows the user to deliver better work with a higher efficiency as well.

Standard for the future

Admittedly, the new pump with XVARI^® Technology has the same functions as the conventional air/hydraulic pump technology, but offers the user several unique advantages. For example, with the ergonomic design an important advantage has been achieved with respect to the conventional models. Furthermore, with the XVARI^® Technology, an optimally controllable oil flow is possible for the first time, so that the cylinder movement can be controlled more accurately, both during advance and retraction. And thirdly, with the higher hydraulic delivery, the operator can work considerably faster. In brief, the new pump with XVARI^® Technology means the end of the more than 50 years hegemony of the time-honoured hydraulic pumps with linear air motors.