H&P What makes you so sure that those days are gone, and what is a "savvy user"?

Swisher: World-class hydraulic users know that zero-leak components and systems are a given from this time forward. These savvy users are well aware of the many advantages of zero-leak systems. They also know that the cost of not insisting on zero-leak performance shows up in disposal costs, service calls, and dissatisfied or lost customers.

H&P: What techniques do these savvy users employ to achieve zero-leak performance?

Swisher: Early on I was asked to define zero leakage in order to have a measurable benchmark. To focus on the issues of achieving zero leakage instead of semantics or words, I stated: "Zero leakage means less than one drop in five days with no visible oil present at any interface during first inspection." In our world-class machines, we expect continuous improvement and will find it necessary to refine this definition even further.

Zero-leak performance occurs when all elements of the hydraulic systems are designed, installed and maintained behind a zero-leak attitude. Let’s talk about some prime examples. First, design machine operations to minimize shock. As you might imagine, shock and vibration can cause fittings to loosen or in some cases, fail. With today’s technology, there is no reason to accept harsh hydraulic control. Programmable velocity and acceleration ramps via electrohydraulic valves in open-or closed-loop control are readily available. Even something as simple as applying soft-shift directional valves can make a significant contribution toward reducing shock.

H&P: Wouldn’t this reduce shock in the hydraulics benefit the basic mechanical integrity of the machine as well?

Swisher: Absolutely. Incidentally, some of the things done to reduce sound levels of machines also promote zero-leak integrity. Pulsation dampers in pump outlets, vibration suppressing clamps for rigid tubing, and the strategic use of hose to minimize pumping pressure pulsations all work to absorb vibration and shock. The result is a quieter, longer lasting, zero-leak machine.

H&P: Please continue; what are some other techniques?

Swisher: Printed circuits for hydraulics, often called hydraulic integrated circuits, dramatically enhance the progress toward zero-leak performance. These are compact circuits with no external plumbing between control valves because valves are contained within an aluminum or steel manifold block. Reducing the number of dynamic seals in favor of static seals can also be a real plus. Using submerged, in-tank pumps or integrated pump-motor packages eliminates the threat of pump shaft leakage.

H&P: What about the choice of fittings? The industry offers a large variety.

Swisher: Yes indeed. But some leaks result from that large variety! Larger plants are commonly faced with a number of different manufacturers’ machines with a need to stock various fitting styles to service them. The inevitable mixing of two different but connectable fittings guarantees a leak.

H&P: So what fittings do you recommend for a zero-leak system?

Swisher: Choose hydraulic fittings that use elastomeric sealing and select the best ISO standards. Use elastomeric seals at every interface-specifically ISO 6149 straight thread, O-ring ports, ISO 8434-3 O-ring face steal fittings, and ISO 6162.2 four-bolt, O-ring flange connections. The consensus of opinion is that an elastomeric seal versus metal-to-metal sealing provides the best overall zero-leak performance.

Incidentally, it should go without saying that there is no place in world-class hydraulic circuits for tapered threads. Using pipe threads in a modern hydraulic system would be like trying to build a modern computer with a 286 or older processor. It may be a cheap answer initially, but the continual poor performance will make you regret your short –sighted decision over and over until you inevitable retrofit the system with O-ring style fittings.

H&P: What do you see the hydraulic system of the future to be?

Swisher: Our company’s retired vice president of technology, Jim Bloomquist, described the hydraulics of the future well by drawing the comparison to refrigerators and air conditioning systems. First, the hydraulic fluid will be in a sealed reservoir and invisible to the machine user. The reservoir will be very small compared to those sized by the traditional rule of thumb. For stationary applications, instead of sizing reservoirs at 5 to 6 times the pump output flow in 1 minute, they will be about 1/10 the pump delivery per minute instead of equal to the pump flow output in 1 minute.

H&P: Now wait a second! The reservoir traditionally has been used as a heat dissipater, contamination settler, and air removal device. How do you accomplish these functions with such a small reservoir?

Swisher: Aeronautic applications of hydraulics have correctly earmarked the reservoir’s role in the circuit by calling it a volume compensator. Its sole function is to allow for changes in circuit fluid volume due to actuators extending and retracting and volume variations due to temperature changes. This will be the only role a reservoir-of-the-future plays.

Heat removal in the circuits of the future will be via heat exchangers of various types. It will no longer be appropriate to accomplish this through sheer volume of fluid residing in a tank. Contamination removal will be done by good filtration systems typically designed in as a low pressure kidney loop for heat and contamination removal.

Air removal is also key. A lesson from automotive brake systems and air conditioning systems serves well here! Air in a newly built hydraulic circuit will be evacuated before hydraulic fluid is added. The sealed reservoir system will not have an air/oil interface but rather a bladder interface. A small, positive, bias pressure will be present and monitored by sensors to notify the machine controller of any fluid volume loss.

H&P: So in summary, then, it sounds like zero-leak performance requires a commitment from not only the machine builder, but users and component suppliers as well.

Swisher: Absolutely. None of the participants can achieve zero-leak performance single-handedly. It is also not possible to pick one element and expect a cure-all for the entire circuit. By this I mean, the thinking, "Well, I will change all my seal material from nitrile to fluorocarbon and stop my leaks," will not do it!

A final element, equally important, is awareness-awareness that hydraulic systems don’t have to leak and an awareness of how to successfully apply these techniques to achieve zero leakage. It’s not an easy goal to attain, but zero-leak hydraulics is definitely a reality!