Oil Seal 20mm

Double-lip oil seal fitted on the 12mm plunger in the pump drive mechanism. 3 pieces are used per pump – one for each plunger.

Application

The seal sits in the drive mechanism housing plate, at the point where the plunger passes from the oil chamber (containing the cam and thrust bearing) into the rest of the pump. It prevents leakage of the oil lubricating the mechanism during the plunger's cyclic reciprocating motion.

Symptoms – when to replace

• Visible oil leak around the plungers, especially while the pump is running.
• Falling oil level in the drive mechanism despite no leak at the housing plate joint (see also O-ring 83x2, 43039).
• Oil traces on the pump housing around the plungers, visible after the machine has stood idle for a while.
• The seal is hardened or damaged when the drive mechanism is disassembled.

How to choose the right part

Selection is based on reference number 43081 and the 12x20x6/5mm size, matched to the 12mm plunger – do not use in pumps with plungers of a different diameter.

Since these seals work dynamically and wear out faster than the static O-ring 83x2 (43039) in the same mechanism, it's worth starting diagnosis of oil leak symptoms with them first. When replacing, it's also worth topping up or replacing the oil in the chamber at the same time (approx. 0.25l of 15W40 oil in the smaller pumps of this type).

[faq]

Do all 3 seals need to be replaced at once, or can they be replaced individually?|They can be replaced individually, but since all three work under identical load conditions, with a visible oil leak it's worth assessing all three while the drive mechanism is already open.

How can I tell if the oil leak comes from these seals rather than from the 83x2 O-ring (43039) on the housing plate?|Leaks from the plunger seals usually appear around the plungers themselves while the pump is running, while a leak from the 83x2 O-ring shows up rather at the joint between the housing plate and the pump housing. If in doubt, it's worth replacing both together, since the parts cost is small compared to disassembling again.

How much oil is needed to top up after replacing the seals?|For the smaller pumps of this type, roughly 0.25 liters of 15W40 oil – however, it's best to check the exact amount on the sight glass or dipstick for the specific model rather than estimating by eye.

[/faq]