It is perhaps useful for professional users to appreciate that chemical resistant is not a one-size-fits-all description. Depending on the pump construction and the materials used for the seals, a sprayer will be suitable with different chemicals.
Viton seals - this will be most commonly what you get with a chemical resistant spray. There is definitely improved chemical resistance compared to more generic seals but one should note that viton is probably best for acidic and moderately alkaline products. In high caustic alkaline conditions, it can break down and care should be taken.
EPDM seals - these are most appropriate to alkaline products and, from my point of view, this should thus be most routinely applied to car care. The majority of car care products are on the alkaline side, necessarily so because the majority of soils are acidic in character. One could equally argue that such seals should not really be used with acids so care must be taken because many industrial wheel cleaners are strongly acidic.
Nylon pumps - this is an addition which is not routinely included in sprayers due to the additional cost. In most instances, this is un-neccesary - most notably water based products. However, if one is using solvents which would include products like tar removers, lubricants or fuels, a nylon pump is essential since normal pump construction will swell in such conditions and become under-performing or non-operational. The norm will be that a nylon pump on a product will be accompanied by viton seals.
In practice, a professional user should probably keep two or even three sprayer types: i) Viton for acids and generic chemicals, ii) EPDM for use with strong alkalines and iii) Nylon pump/viton seals for use with solvent based products (iii is perhaps less appropriate to you guys since tar removers are not as routine as here in the UK).
Hope that helps someone out there!
