Liquid purification or separation – Flow – fluid pressure or material level – responsive – Fluid pressure responsive by-pass
Patent
1997-04-17
1999-03-30
Drodge, Joseph W.
Liquid purification or separation
Flow, fluid pressure or material level, responsive
Fluid pressure responsive by-pass
55323, 210136, 210168, 210184, 210338, 210443, 210456, B01D 3514, B01D 35143
Patent
active
058883835
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of International Application No. PCT/GB95/02725, filed on Nov. 23, 1995.
This invention relates to fluid filters particularly, but not exclusively for use with internal combustion engines. The use of meshes and/or screens for removal of debris from a fluid stream such as re-circulating engine oil is known. Both metallic and non-metallic filter materials are used; the filter elements may be cleanable or disposable. It is usual to pass all of a fluid stream through the filter arrangement; this is a "full flow" filtration system.
Debris in a lubricating oil system takes several forms. There is particulate mechanical debris present in a new engine in the form of metal particles which are flushed from the oilways when the engine is first started. There is also fine debris such as combustion by-products and dust which progressively contaminate the oil as the engine runs. The former debris is potentially very damaging, the latter needs to be controlled to prevent build-up inside the engine and a particularly effective way of addressing this is to utilise a centrifugal cleaner in conjunction with a conventional "full flow" static filter. The usual arrangement is for about 5-10 percent of the total oil flow to pass through the centrifugal cleaner whilst the rest passes through the static filter, in the usual full flow configuration. The centrifugal cleaner is extremely efficient in removing fine debris, particularly combustion by-products.
The use of both disposable and cleanable filter elements in such a full-flow system is very old. However, the choice of filter pore size is important since the use of too small a pore size will rapidly result in clogging by fine contaminant particles, leading to an increase in back pressure and eventual failure. Too large a pore size will leave fine contaminants unaffected. In practice, the use of a single small pore size disposable filter element for both coarse and fine contaminants has become the norm, but such elements inevitably require periodic replacement or cleaning. But in automotive lubricating oil systems, it is known that the majority of the damage due to particulate mechanical debris occurs very early in the life of the engine.
It has been proposed to use a static full flow filter with two filter elements of different pore sizes disposed in series, together with valve means operable to by-pass the filter if it becomes excessively obstructed. Such an arrangement is disclosed in U.S. Pat. No. 4,885,082. However, in the event of obstruction, the whole filter is by-passed except for a small proportion of the flow. Inevitably, this results in the majority of the flow being completely unfiltered in the event that the by-pass valve means operates.
It is an object of the present invention to provide a simplified construction which avoids this disadvantage.
The present invention provides a full-flow fluid filter assembly characterised by the inclusion of a large pore size screen and a small pore size screen which in use are disposed in series with one another and with the fluid flow, together with means responsive to obstruction of the small pore size screen to cause substantially all of the fluid flow to pass only through the large pore size screen the arrangement being such that, in use, all of the flow passes through at least one screen. The means responsive to obstruction of the small pore size screen may be a one-way valve adapted to respond to increased back pressure developed across the small pore size screen. When the back pressure reaches a pre-chosen level corresponding to an unacceptable level of small pore size screen obstruction, which may in turn correspond to an unacceptable reduction in fluid flow, the valve opens to by-pass the small pore size screen. A spring loaded one-way valve is particularly preferred. Thus in the filter assembly of this invention, there is always at least one filtering element in operation, even when the valve means operates to by-pass the small pore size screen.
In the present context and for the purposes of t
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Drodge Joseph W.
The Glacier Metal Company Limited
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