The condition of a hydraulic system, as well as its probable future performance, can best be determined by analyzing the operating fluid. Of particular interest are any changes in the physical and chemical properties of the fluid and excessive particulate or water contamination, either of which indicates impending trouble.

Excessive particulate contamination of the fluid indicates that the filters are not keep­ ing the system clean. This can result from improper filter maintenance, inadequate fil­ ters, or excessive ongoing corrosion and wear.

1. All samples should be taken from circulating systems, or immediately upon shutdown, while the hydraulic fluid is within 5T (9°F) of normal system operating temperature. Systems not up to temperature may provide nonrepresentative samples of system dirt and water content, and such sam­ ples should either be avoided or so indicated on the analysis report. The first oil coming from the sampling point should be discarded, since it can be very dirty and does not represent the system. As a general rule, a vol­ ume of oil equivalent to one to two times the volume of oil contained in the sampling line and valve should be drained before the sample is taken.

2. Ideally, the sample should be taken from a valve installed specifically for

sampling. When sampling valves are not installed, the taking of samples from locations where sediment or water can collect, such as dead ends of piping, tank drains, and low points of large pipes and filter bowls, should be avoided if possible. If samples are taken from pipe drains, sufficient fluid should be drained before the sample is taken to ensure that the sample actually represents the system. Samples are not to be taken from the tops

of reservoirs or other locations where the contamination levels are nor­ mally low.

3. Unless otherwise specified, a minimum of one sample should be taken for each system located wholly within one compartment. For ships’ systems extending into two or more compartments, a second sample is required. An exception to this requirement is submarine external hydraulic systems, which require only one sample. Original sample points should be labeled and the same sample points used for successive sampling. If possible, the following sampling locations should be selected:

(a) A location that provides a sample representative of fluid being supplied to system components

(b) A return line as close to the supply tank as practical but upstream of any return line filter

(c) For systems requiring a second sample, a location as far from the pump as practical Operation of the sampling point should not introduce any significant amount of exter­ nal contaminants into the collected fluid.

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