Ah! I knew I had seen it somewhere - I've been trying to work out where.
Quote from my tractor manual (Chamberlain 306) :-
"If a clean dry compressed air supply is available, a stream of air may be directed against the inside of the element. Pressure must not exceed 100psi and the nizzle kept a reasonable distance from the paper.
Obstinate dirt can be removed by washing the the element in warm (120-140F) solution of water and non-foaming detergent. Rinse clean and dry after washing. Do not dry with compressed air."
John

