Working on hydraulic equipment can be dangerous, especially if you are not well-learned in the technology. A load suddenly and unexpectedly moving can cause serious injury or worse. The hydraulic fluid itself also poses serious potential dangers. Fluid in a working hydraulic system is often hot enough to cause serious burns from pipework or the fluid itself.
However, even greater potential danger is posed by pressurized fluid. Even at moderate pressure, a jet of fluid shooting from an opening in a hydraulic system can easily penetrate the skin. Problem is, injuries of this type initially may not appear serious because the fluid entry site can be very small. The danger lies with the injury that has occurred below the skin. Even if immediate treatment is performed, fluid injection injuries can cause tissue damage, infection, toxicity reaction, amputation, and even death.
And this is just with hydraulic systems at moderate pressure. The potential dangers become more pronounced with high- and ultra-high-pressure (in excess of 10,000 psi) hydraulics. Kenneth Kjellberg, Divisions Manager, High-Pressure & Engineering at CEJN AB, Skövde, Sweden:
Success in using ultra-high-pressure (UHP) hydraulics in applications such as rescue tools, bolt tensioning, and hydraulic torque tools is highly dependent on a flexible hose and quick-coupling technology. Imagine a situation where a ship’s mechanic needs to tighten a bolt on a large ship engine in the confined space of an engine room and you can immediately see the need for and importance of a fast and reliable connection method. To install an application with six to eight tensioners and then have to fit hard piping between them would be quite a time-consuming process requiring several hours of bending, cutting, threading steel tubes.
Effects of High Pressure
The reason for such extreme pressures is, of course, to make components as light and compact as possible. Because force is the product of pressure and area, doubling the pressure allows reducing the area by half while still applying the same force from a tool or other machine. This simple correlation has led UHP equipment users to demand higher and higher pressures.
Of course, when a hydraulic system is pressurized to this extreme, it also results in extreme levels of stress in materials. To avoid any risk of injury to users, materials and heat and surface treatments must to be carefully tested to ensure the proper combination of surface hardness and toughness to withstand the required number of pressure cycles without material fatigue.
This is especially true of quick-acting couplings, where materials must not only withstand continual pressure cycles, but also tolerate repeated connection and disconnection. Hose and quick connect technology now allows us to establish such a connection in just a couple of minutes — even at pressures to 400 MPa
Safety is a key concern with any connection between a hose end and the coupling/nipple. The higher the pressure, the more reliable the connection must be. In the lowest pressure range of UHP hydraulics it is quite common to use NPT thread connections sealed with Teflon tape or liquid sealant. For straight threads, such as BSP, a bonded rubber metal seal ring is also common. For pressures exceeding 100 MPa, emphasis is placed on minimizing the pressurized area and avoiding the use of tape, sealants, or washers.
Safe and Effective Sealing
The proper method is to use a metal-to-metal sealing cone. Most cone systems have a male and female shape that must be manufactured using special cutting tools. In the early 1980s CEJN developed a sealing cone, which is still manufactured today, that fits against a normal 120° drill cone. Using the standard drill cone and a CEJN Metal Seal (CMS) adapter creates a safe and cost-effective seal. The CMS port dimensions are free for anyone to use.
A regular maintenance schedule is vitally important to user safety for these UHP systems. Of course, the potential for accidents increases as machines wear with age, especially if they contain some obsolete design characteristics or have not been well maintained.
To help users recognize unsafe practices and work safely around high-pressure hydraulic and other fluid systems, CEJN industrial Corp. offers a free, 20-page manual titled, “Safety Guidelines for Ultra High-Pressure Hydraulic Applications.” Go to bit.ly/HP516CEJN to download a copy, or visit www.cejn.us for more information.