Piston Spring 3,0x29x40mm

Compression spring fitted behind the plunger in the pump drive mechanism. 3 pieces are used per pump – one for each plunger.

Application

The spring presses the plunger against the cam via the pressure plate, maintaining constant contact between the plunger and the cam surface as the drive mechanism rotates. It provides the smooth, cyclic reciprocating motion of the plunger needed to generate pressure in the pump.

Symptoms – when to replace

• Drop in working pressure during operation, despite sound plunger seals and valve block.
• Uneven, pulsating pump operation noticeable on the pressure gauge or at the gun.
• The spring is visibly shortened, broken or deformed when the drive mechanism is disassembled.
• Knocking or a metallic sound from the drive mechanism during pump operation.

How to choose the right part

Selection is based on reference number 43040 and the 3.0x29x40mm size – the springs are sold individually, but if one is worn it's worth checking the condition of the other two, as they work under the same conditions and usually wear out around the same time.

When replacing the spring, also assess the condition of the 14mm pressure plate (43.041) and the plunger (49.021) in the same assembly – a weakened spring accelerates uneven wear on these neighboring parts.

[faq]

Do all 3 springs need to be replaced at once, or can they be replaced individually as they wear?|They can be replaced individually, but since all three work under the same load conditions, replacing only one while the other two show visible wear usually leads to another replacement shortly after.

Does the new spring need to be installed in a specific orientation?|The spring has no defined installation direction – what matters is that the pressure plate is correctly seated on its plunger-facing side, so that the pressing force transfers evenly onto the plunger.

[/faq]