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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).
Investigation into the failure of S.U. petrol pumps on a Bentley, attributing the issue to poor quality diaphragm cloth and the use of Discol fuel.

Identifier  ExFiles\Box 149\4\  scan0201
Date  26th February 1937
  
Rm{William Robotham - Chief Engineer}/Gry{Shadwell Grylls} from Rm{William Robotham - Chief Engineer}/JBD{John B. Dixon - Fuel Systems}

Rm{William Robotham - Chief Engineer}/JBD{John B. Dixon - Fuel Systems}1/M.26.2.37.

S.U. Petrol Pumps on Mr. Lappin's Bentley.
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These pumps were fitted here on the 10th September last year, since when the car has done 10,677 miles running on Discol. The car was recently fitted with a trial switch, when one side of the pump was found to be out of action.

On arrival here both sides of the pump were working but blowing out discol from the vent holes.

The diaphragms, which were some we received before the G.5 material was standardised, were of poorer quality cloth, thinner and not so well impregnated as that which we waited for and subsequently put on production. This poor quality diaphragm has also become porous on petrol in two cases.

On examination both diaphragms were very porous with very little dressing left in the cloth especially on the inside faces where it appeared to have been partially dissolved and rubbed away leaving small lumps of dressing built up on the edge fixed to the armature. One side showed signs of the armature having fouled the side of the magnet pot which would explain the temporary failure. This is caused by the pole piece not being central with the magnet pot and giving a heavy side load which is only taken by three of the distance pieces. These distance pieces wear locally, the wear being aggravated by the petrol or discol which was leaking through the diaphragm.

To overcome this trouble we have arranged that the magnet assembly is checked for eccentricity of the pole piece by the S.U. Company.

With regard to the diaphragm trouble we attribute this mainly to the poor quality cloth and although discol is known to affect the present G5 we should be able to expect considerably better service life in spite of the Discol with the present material.

We have four diaphragms still running endurance on a test rig on Ethyl petrol which have run for 400 hours without an involuntary stop pumping at 80 pints per hour.

Rm{William Robotham - Chief Engineer}/JBD.{John B. Dixon - Fuel Systems}
  
  


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