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Should I use hose or hydraulic tubing when plumbing my system?

A: There are advantages and design concerns for both.  For example:

  • Hose is more expensive than tubing, on a foot per foot basis
  • Hose absorbs and dampens vibration better than tubing
  • Tube assemblies require more expertise to fabricate than hose assemblies
  • Hose assemblies have temperature and fluid compatibility limitations
  • Tubing typically looks “neater” in a system than hose does
  • Hose requires much less time to fabricate and install than tubing does
  • Tubing typically has a smaller overall envelope size than hose

Are forged tube fittings better than brazed styles?

Yes.  Forged fittings are inherently stronger than brazed styles.  A forging is formed from a single piece of metal.  A brazed fitting is made up of two or more separate parts.  Therefore, the possibility of leakage or failure at one of the braze joints can be a concern.

What is the most reliable sealing method for hydraulic fittings?

Elastomeric.  Metal to metal seals such as pipe threads on port connections and flared or flareless connections on tube/hose connections have been around for years.  They work well at low to medium pressures but can leak after time due to a variety of reasons.  Elastomeric seals such as SAE straight threads on port connections and O-Ring Face Seal or SAE flanges on tube/hose ends absorb vibration and compensate for minor surface imperfections which result in a better seal.

How do I troubleshoot a leak in my hydraulic system plumbing?

Following these steps should help correct most leakage problems:

  1. Shut down the system, use lock out/tag out if possible and bleed any residual pressure from the system.
  2. Find the true source of the leak.  Oil can drip and run from one location to make it look like its coming from a fitting.
  3. Determine where the oil is really coming from.  If the leak occurs where a hose fitting or tube assembly connects to an adapter, check to see if the connection is tight.  If the swivel nut is loose, re-tighten it.  Do not over-tighten.  If the leak occurs where the adapter threads into a component, again check to see if it is loose and re-tighten.  If the leak persists in either of these cases, remove the fitting, inspect the sealing surfaces for damage or contamination and replace it with a new fitting.  Tighten appropriately.  Do not over-tighten.

What are the recommended fluid velocities for hydraulic lines?

  • For pressure lines, maximum recommended fluid velocity is 20 ft/sec
  • For return lines, maximum recommended fluid velocity is 10 ft/sec
  • For suction lines, maximum recommended fluid velocity is 4 ft/sec.

How can I reduce the amount of noise in my hydraulic system?

Following these guidelines should help reduce the amount of noise experienced: Use hose in place of hydraulic tubing where appropriate. Hose can dampen vibration and thus reduce system noise.  Use clamps having plastic or elastomeric inserts on tubing and hose to help absorb vibration.  Size components and plumbing properly.  Undersized components and plumbing result in high fluid velocities and turbulence that result in vibration and noise.  Try to design pump to reservoir relationships so as to avoid aeration and cavitation in the pump.  If space permits, build and insulate an enclosure around the power unit.  Mount pump/motor combinations on rubber mounts to dampen vibration.

Is it necessary to clean out a hose or tube assembly before installing it?

Yes.  Contamination is the leading cause of problems in hydraulic systems.  Hose and tube assemblies should be blown out with filtered shop air or flushed and blown out with a solvent which is chemically compatible with the hose material.  The ends of the hose and tube assembly should be capped and/or plugged until the assembly is installed.

What’s the difference between a hose’s working and burst pressure?

A hose’s published working pressure is the maximum pressure the hose should see while in service.  This includes any spikes that may occur during operation.  A hose’s published burst pressure is the value at which a brand new piece of hose will fail at during a one time pressure test.

If I have a hose that’s rated at 3,000 psi working pressure and has a published burst pressure of 12,000 psi, why can’t I use it in a 3,500 psi system?

Hose manufacturers give hoses working pressures and burst pressure.  These are typically at a 4:1 ratio (not safety factor) to each other. When choosing a hose for a system, select a hose that is rated at or above the maximum pressure that can occur in the system.  Often times, these values may be higher than the relief setting.

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