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From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Letter discussing the analysis of a failed engine oil filter, its deposits, and potential causes for its collapse.

Identifier  ExFiles\Box 145\1\  scan0196
Date  27th April 1937
  
TELEPHONE
WHITEHALL 1010.

[Handwritten Signature: Lodge, Swatt]

[Handwritten note: Filter of 3217 at 1500 miles]

CAXTON HOUSE EAST,
WESTMINSTER,

LONDON, S.W.1.

27th April 1937

S. H.{Arthur M. Hanbury - Head Complaints} Grylls Esq.,
Messrs Rolls Royce Ltd.,
DERBY.

Dear Mr. Grylls,

In regard to the filter which you forwarded us after 1,500 miles running on MOBILOIL ARCTIC, the deposit was removed from it and only one gram was obtained.

This consisted mainly of carbon, but in the ash there was a percentage of lead, copper and iron as oxides.

Our Chief Chemist points out that if due to internal condensation in the engines, or similar causes, filters of this kind become damp, their efficiency as filters is considerably diminished.

We would also comment on the apparent collapsed condition of the filter, which seems to indicate that either the by-pass valve is not functioning correctly, or alternatively a small amount of carbon of fine texture has considerably diminished the efficiency of the filter, and one wonders whether there is some feature involved which has not yet disclosed itself.

We see no reason for the collapse of the filter, providing the by-pass valve was functioning correctly unless this unit has been operating in a lubrication system different from the normally accepted designs.

We have understood for some time from American experience that the efficiency of cartridge-type filters falls off very rapidly when the materials are of sufficiently close texture that the pores fill up quickly with carbon or metallic oxide deposits.

As there are no simple means of cleaning such filters which are practicable to the ordinary motorist, it would be interesting to learn whether this particular complaint is an isolated one, or not.
  
  


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