A designer’s guide to hose assemblies

By Josh Cosford, Contributing Editor

Like their fitting and adapter brethren, hydraulic hose assemblies are often an afterthought to the hydraulic designer. I’d rather be working on crafting a unique hydraulic circuit as well, but we shouldn’t forget the importance of a holistic approach to machine design. Your fluid power technicians are an essential piece of the puzzle to ensure hoses are expertly crafted and installed, but your forethought goes a long way toward saving costs, easing installation, and improving reliability.

Assuming you’re the hydraulic designer, not the engineer responsible for the machine itself, there are many considerations when planning the hose assemblies. Generally, you must consider three things when selecting and planning your machine’s hose assembly: hose construction, hose end selection, and routing options.

First things first: hose construction

Selecting the correct hose construction style plays the most important role in providing customers with an effective and safe hydraulic machine. Pressure compatibility is the primary factor you must consider when selecting your hose, and your starting point should be the below chart on SAE J517 hydraulic hose standards.

You should select your hydraulic hose based on the maximum working pressure range that your machine experiences. The range takes into consideration the largest diameter (lowest pressure) and the smallest diameter (highest pressure), which are at the heart of hydraulics. By their very nature, small hose handles high pressure more easily than large diameter hose, so check with your hose provider for the pressure rating of the diameter you need for your machine’s flow rate.

All hydraulic hoses are rated for their working pressure, which is half that of proof pressure and half again as high as burst pressure. If your system is prone to pressure spikes, you may need to select a hose rated for slightly higher than your nominal working pressure. Proof pressure describes the point where a hydraulic hose is subject to permanent damage, so it’s best to avoid kissing that demarcation on the pressure gauge.

In many cases, you may want to avoid the venerable 100R1 and 100R2 standards if your machine has a variety of hose sizes while operating at least 3,000 psi. Many machine manufacturers are standardizing on one of the isobaric hose designations, such as 100R17, where every hose from 3/16 to 1 in. is rated for 3,000 psi. Their rising popularity has reduced production costs, as many hose manufacturers have scaled up to this design.

If you require large-bore hose and at higher than 3,000 psi, you’ll have to explore options like 100R12, 100R13 and 100R15, which employ spiral-wound reinforcement wires with four or six layers. Some people suggest you choose a hose rated for 25-50% above your working pressure, but in reality, the strict hose guidelines already account for pressure spikes, and manufacturers build accordingly.

Flow considerations

After settling on a hose construction type, you’ll need the diameter that best suits the flow. Remember to factor in unique situations, such as differential cylinders and the additive flow generated out of the cap port during retraction. In cases where the area ratio is high, you may observe more than double the flow rate, so be sure the hose is sized appropriately.

There is no absolute description of flow capacity for a hydraulic hose because four scenarios determine the maximum fluid velocity, which is usually our limiting factor rather than something harder to calculate, such as pressure drop. Starting on the low end, prevent excessive velocity through suction lines, where vacuum could result in the spontaneous gas bubble formation we call cavitation. As a rule of thumb, never let suction lines exceed 3-4 ft/sec; lower is always better, so there’s no harm in aiming for 1 ft/sec if the space allows it.

Also, ensure case drain and pilot lines are limited to 1 ft/sec velocity or slower. Under no circumstances do you want to risk damage to pump internals or controls. You can be more liberal with velocities of pressure and return lines, for the most part. Pressure lines, such as pump pressure and working lines, can range from 20 to 30 ft/sec and depend on pressure. Higher pressure systems are more suitable for higher velocities because less fluid is lost as pressure drop relative to maximum pressure. For example, running 30 ft/sec in a 4,000 psi system is less problematic than running 30 ft/sec in a 1,000 psi system.

Take note that return lines should also be sized to limit velocity, although not as much as suction lines. It’s reasonable to operate around 6-10 ft/sec in this case, and the primary goal is to limit back pressure in the tank lines of valves and case drains, but also prevent excessive pressure at return filter housings. Some consideration should be given to line size despite the ideal fluid velocity. Small lines are more naturally prone to pressure drop, so be sure to avoid very small suction, pressure and return lines even if they fit within the ideal velocity range.

Small hose ID is subject to higher friction forces from the fluid disproportionately running through the boundary layer. Conversely, a larger hose allows flow through the center and away from the inner tube walls. As well, return and pressure lines are more likely to experience turbulent flow and energy dissipation, leading to pressure drop. When in doubt, don’t cheap out on diameter and risk the trouble resulting from undersized hose assemblies. In practice, when making a set of hose assemblies for a hydraulic machine, it’s common to see a 2 in. suction hose, a 3/4 in. pressure hose, a 1 in. return hose, and a 1/2 in. case drain hose.

Don’t overlook hose ends

We’ve now finalized the construction type best suited to our machine’s hydraulic pressure and refined our internal diameter to suit system flow; we must now choose our hose ends. You’re a hydraulic designer in 2025, so let’s cut the bull; we’re only going to select leak-free connections using synthetic rubber seals. Sorry, NPT and JIC — you’ve been great, and I cherish all our memories, but it’s you and not me. O-ring Face, O-ring Boss and flanges offer so much more in this relationship.

ORFS has quickly become the connection of choice, offering all the benefits of the JIC style with a leak-free connection. It is available in a variety of sizes, with 45° and 90° hose-end bends, and the female ends are swivel-equipped for ease of installation. The easily replaceable O-ring is located on the face of the male end, making service work quick when leaks do occur.

Flange fittings, such as the common SAE Code 61 and Code 62 styles, are commonly used for high-pressure and/or high-flow connections. The split-flange connections allow the technician to align the hose end appropriately to avoid binding or twisting, and, like the ORFS fitting, the O-ring resides on the male end (there is no “female” flange because the males attach to the flat connection surface where the port is located).

Typically, the O-ring boss type fitting is used as an intermediate connection to the hose end. Similar to BSPP or Metric, these use a polymer seal situated at the top of the port thread, sealed by a cavity within the port thread (ORB) or through a bonded washer (BSPP and Metric). However, ORB is rarely used as a hose end because the male fitting requires an expensive live swivel. They’re out there and available in straight or 90° orientation, but many designers prefer female hose connections.

To mitigate the hate mail, I should mention that some machines happily use JIC and NPT fittings, and that’s perfectly fine. However, this designer’s guide is biased toward superior technology, and I’d be remiss not to push anything other than hose ends with replaceable seals. ORFS and flange fittings are simply better, so get with the times and use them. So, despite the fact that JIC is easy to use with tube-flaring systems, many manufacturers offer two-piece tube connections for ORFS, and flange fittings can also be welded to tubes. Besides, this article is really about hose assemblies, not tubed plumbing.

Layout and routing

The final consideration for hydraulic designers pertains to the physical layout of the hose assemblies on the machine itself. Hoses deserve better than simply the joining of point A to point B. Their orientation, layout and fitment must prevent friction wear, excessive joint pressure and twist/torque forces. Pictured are various incorrect and correct methods to mount hydraulic hose assemblies to prevent bending at the crimp joint. The weight of the hose should never encourage bending at the point where the steel hose end pinches the hose cover. If a hose’s weight causes sagging, use 90° hose ends to support the bend and let the hose hang naturally.

The hose length should be sufficient to prevent stress during connection and tightening, but not so long as to rub or vibrate against any hose or other surface. Long runs of hoses need to be clamped against the machine using one of many technologies. Manufacturers offer blocks, saddles, clamps, and various technologies, welded or bolted to the machine, to neatly clamp the hose down.

When installing hose lengths on such systems, be sure to avoid excessive tightening of both the clamp or the hose between connections. To manage the cycles of pressure and temperature, there should be a slight slack between each connection point while preventing excessive clamping that could damage the cover or reinforcement layer. Where hoses cannot be prevented from rubbing against hard surfaces or other hoses, install each hose with protective wrap designed to reduce wear and friction. These can also protect against ambient or environmental damage, such as industrial fallout or UV rays, and should also be used when hoses are routed inside channels or beams.

When the hydraulic designer views their role as comprehensive, every layer of machine design — from the original schematic to the finished product — should be intelligently planned and organized for the most efficient, economical, and effective design possible. Hose assemblies seem elementary, but the rest of the machine matters little when burst or damaged hoses plague your hydraulic system.