Typically, one of the last things that designers of machines using fluid power think about is the hose and where it goes. Yet, machine safety, performance, and reliability all depend on proper hose placement and routing. Here are ten things to consider-before finalizing placement of major components such as electrical and fuel systems-that will help your equipment run better than ever.
1 Minimize hose twisting. Twisting high-pressure hose by even 7 degrees reduces service life by as much as 90%. If hose must flex, look for a pivot point or place the hose can hinge. Otherwise, the hose may form an S-Shape. This type of bend results from hose that is pushed rather than bent. The problems with S-bends are a reduction in overall service life and excessive hose movement. If high-pressure hose must go around several turns, break the hose into sections with connectors so that it bends in only one plane.
2 Consider rotary vs. reversing motion. If rotary motion of the hose is a continuous 360 degrees , use a rotary joint. If the required movement is reversing, a swivel joint is preferable. Remember that swivel joints help avoid hose twisting and bending at the fittings.
3 Pick suitable hose clamps. Common sheet metal clamps will not hold high-pressure hose. The clamp should be 1/32 of an inch smaller than the outside diameter of the hose. Never clamp a hose on a bend.
4 Specify the appropriate hose length. Although any hose should have a little slack, excess hose increases pressure drops. Not enough hose and the system is likely to fail at fittings and at leading points. Plan for the hose to possibly stretch up to 2% in high-pressure applications.
5 Make the system as leak-proof as possible. Since each connection is a potential leak point, minimize the number of them.
6 Make the system accessible for maintenance. Carefully consider the placement and positions of ports, valves, filters, heat exchangers, fluid reservoirs, and other system components to which maintenance and service technicians must have access. Design the hose placements so that they run parallel within the equipment and follow the contour of the machine.
7 Accommodate reciprocating motion.
If the hose has to reciprocate, consider the following approaches: Rolling-Arrange the hose in an unbalanced U-shape with one leg stationary and longer than the second. The second leg is free to reciprocate; Hose reels-Equipped with swivel joint and a spring for rewinding hose, these help accommodate reciprocating motion; Hanging-With this approach, hose hangs in loops from supports. As one end of a loop moves away from the other, the other loops adjust to the changing center-to-center distance.
8 Beware of hazardous fire conditions. Consider hydraulic lines in relation to hot areas where a burst hose spraying hydraulic fluid could start a fire. Designs should include routing lines through metal tubing or having sheet metal serve as a baffle.
9 Minimize risks from whipping hose. If a pressurized hose blows apart, fittings can be thrown at high speeds. Loose hose can flail or whip with great force. When the risk exists, consider guards and restraints to protect against injury.
10 Consider temperature and environmental factors. External heat sources should not raise the temperature of the hose above its maximum operating temperature. Select heat shields, sleeving, or other methods of avoiding hose damage from external heat. Conditions to evaluate include exposure to ultraviolet light, salt water, ozone, abrasion, electricity, and air pollution.
The following individuals contributed information for this article: Mike Miller, director of training, Aeroquip Industrial Group; Jerry Devan, director of Aeroquip's test lab; Dennis Skemper, applications engineer, Gates Rubber; Dick Medvick, mechanical engineer, Swagelok; and Lou Moreiras, director of engineering, Parker Hannifin's Hose Products Division.
A published report from the Society of Automotive Engineers, SAE J1273, contains additional recommendations for safe and effective use of hose and fittings. The report is available at www.sae.org/products/j1273vid.htm. SAE also offers a video depicting recommended practices for hydraulic hose assemblies. For more information, call (724) 772-7148.