Although oxidation is the greatest contaminator in a hydraulic system, many other contaminants exist. All contaminants can be controlled through the use of chemicals and good maintenance procedures. The best control of course is through the use of good maintenance. Maintenance procedures can always be checked accurately, whereas chemical stability cannot.
Dissolved Air
The air solubility of liquid is its ability to absorb or dissolve air at any pressure higher than a vacuum. The term “dissolve” is used because the air bubbles are very small and are distributed completely through the fluid. Air is picked us when the pump suction filter is exposed to the air in the reservoir or through leaks in the suction piping or pump packing. Air can also set into the system if foamy oil is picked up by the pump suction inlet or if the oil reservoir is open to the outside air.
As previously pointed out, air that remains in solution oxidized the fluid and causes problems at those points in the system where sudden pressure-drops occur. When hydraulic fluid has a considerable amount of dissolved air in it, foam may come out of the return lines to the reservoir because of the low pressure that exists in the return lines. This foam can be eliminated with screens or splash plates.
Foaming
Although all fluids are susceptible to foaming to foaming, the amount of foam in a system can be reduced to a minimum by the addition of chemical foam depressants. These additives do not prevent air from dissolving in a fluid or prevent foam from forming when air pressure is suddenly reduced. A foam depressant forms unstable foam with larger bubbles that break up faster once it has broken out of the fluid. This reduces the total amount of foam that is formed. As a result the amount of foam that accumulates in the reservoir can be held down to a comparatively thin layer
No comments:
Post a Comment