Fluid Power - Learn the Terminology

Burst Pressure - The pressure that causes rupture.  Reference pressure intended for destructive testing purposes and design safety factors only.

Fluid Power - Learn the Terminology

Buffing: The partial removal of the hose cover in order to put on a coupling. A stone wheel is typically used to grind or buff the cover to remove the cover material.

Learn the Terminology

Cut-Off Length:  The length of that part of the coupling not directly in contact with or applied to the hose. Subtract the sum of the cut-off length of the two couplings from the total length of the assembly, and you will have the approximate hose-cut length to be replaced.

Dash Size:   A shorthand method of denoting the size of a particular end fitting or the inside diameter of a hose.  Measured in 1/16 of an inch (i.e., -4 = 4/16” or ¼”).

Hose Cleanliness – Methods of measurement Part 2

There are three principal methods to measure the contamination level in a component, circuit, or system:

1) Gravimetric Measurement (ISO 4405)

2) Particle Size Distribution Analysis (ISO 4406 or NAS 1638)

3) Maximum Particle Size Analysis (ISO 4407).

This post will discuss the second method (above).

Particle Size Distribution Analysis (ISO 4406 or NAS1638) 

Particle Size Distribution Analysis is a reporting method to gauge both the size and number of contaminant particles in a calculated quantity of hydraulic fluid.  A fluid sample is either taken directly out of a hydraulic system or a known quantity of fluid is used to dislodge contaminants out of a hydraulic component. This fluid is run through a particle counting instrument to size and count contaminant particles.

These particle ‘counts’ can then be normalized by comparing the total component volume and to a corresponding ISO 4406 ‘code’ level of particle contamination. Levels of five and 15 microns of contamination are reported on a logarithmic scale corresponding to and ISO 4406 ‘code’ for the number of particles greater than or equal to these respective sizes per milliliter of fluid.
 

 

Hose Cleanliness – affects Valves, Pumps, System cooling

Valves: Microscopic contamination (similar to erosion) can mill away tolerances which are used for sealing purposes. On spring centering valves, the debris may get caught between the valve and the wall surface. The contamination will cause the slowing down of the motion of the valve or causing sluggish or adverse mechanical actuation.

Abrasive particles enter the clearances between moving parts they score and hone the surfaces to greater tolerances. As these tolerances broaden, system performance is compromised by pressure losses incurred due to fluid leakage from high to lower pressures.

The worst occurrence is when particles that are greater than or equal in size to the orifice openings become wedged between the two surfaces. The contamination may cause wear to occur or it may cause the system components to seize.

Pumps & drives: Microscopic contamination can mill away material, creating leak points. These leak points rob the hydraulic system of pressure and cause poor responsiveness.

System cooling: Working fluid may not flow through to remove contaminants generated from metal to metal contact when passages become blocked. Lower flow rates mean greater heat buildup in systems and thermal breakdown of the working fluid.

 

Hose Cleanliness - Origin of Contamination

Origins of contamination may be from system components, the hydraulic working fluid, the outside environment, or be generated by the system itself. These contaminants, some large and some microscopic, can have a profound impact on the performance and longevity of the hydraulic system.

There are three principal means through which contamination can

occur in a typical hydraulic system. 

Contamination can be:

1.    Generated during system operation

2.    Built into the system during assembly

3.     Ingested by the system during operation

 The working fluid in hydraulic systems should be as homogeneous as possible and free of all visible and microscopic debris for optimum performance. The complete absence of contamination in hydraulic systems is unrealistic, but an acceptable and defined level of contamination is generally considered hydraulic system cleanliness. The best approach to cleanliness is to prevent contamination in the first place. Use clean hose and couplings and keep them clean (i.e. cap ends). Clean hose bore after cutting to length as cutting hose to length is a major contributor to contamination.

Blast from the Past

This old technical note surfaced recently from a Product Application department discussion.  While dated, it does point out that a good technique for evaluating vibration is to determine if there is vibration present beyond the belt drive system.