EHC Fire-Resistant Oil Ultra-Clean Purification Unit

What it removes

Phosphate-ester EHC fluid is not mineral oil, and it fails differently. This unit removes water, dissolved gas, particulate and -- the part that matters most -- the acid and the varnish precursors that phosphate esters generate as they age. Water in EHC fluid hydrolyses the ester, and the hydrolysis products are acidic; left alone, the acid attacks the servo valves in the governing system and the fluid stops meeting its own specification long before it stops looking like fluid.

How it works

The unit treats phosphate ester on the same vacuum principle as a mineral-oil purifier, but every wetted part is selected for ester compatibility: seals, hoses and filter media that are correct for mineral oil are not correct here, and a unit built for mineral oil will contaminate an EHC charge rather than clean it. Dehydration runs at a temperature low enough not to accelerate hydrolysis. Fuller's earth or an equivalent adsorbent stage removes the acidic breakdown products and the dissolved varnish precursors that filtration cannot reach.

Where it is used

Steam turbine governing systems, and only those. A captive power station whose phosphate-ester fluid was laying down varnish on the servo valves is the reference installation. The same fluid is used in gas turbine fuel control on some frames and in a small number of steel-plant hydraulic systems near furnace areas, where the fire resistance is the reason for the fluid in the first place.

Options and service

Ester-compatible seals and hoses throughout, stated on the drawing. On-line connection to the governing-system reservoir. Adsorbent change-out is a scheduled item; the interval is set from the acid number trend, which is why the unit is normally supplied with sampling points rather than a fixed service interval.