I penned this rebuild treatise some time ago but never got around to publishing it. As it it the silly season I thought that it may relieve the mind-numbing cerebral assault of Xmas and the New Year.
You will never need to attend to one of these lovely little engineering pieces, but you may be interested in what is involved in bringing one back to life.
From it's launch in 1955 until September 1960, the DS19 wasfitted with a ingenious combined water pump and low pressure hydraulic pump.
The water pump was completely conventional and served todistribute coolant around the engine cooling circuit. However, co-axial withand in front of the water pump was a positive displacement hydraulic pump, bothpumps being driven at the same speed by a dual-belt drive.
The hydraulic pump is of the gerotor design (derived from “generated rotor”). The gerotor moduleconsists of an inner and outer rotor. The inner rotor has 4 teeth, and theouter rotor has 5 teeth. The outer rotor is located off-center and both rotorsrotate. The geometry of the two rotors partitions the volume between them intodifferent dynamically-changing volumes. During the assembly's rotation cycle,each of these volumes changes continuously, so any given volume first increases,and then decreases. An increase creates a vacuum which creates suction, andthis part of the cycle is where the intake is located. As a volume decreasescompression occurs. During this period hydraulic fluid under low pressure isdelivered to the hydraulic bloc (or “brain”).
Within the hydraulic bloc this pressure acts on a largediameter piston, and if the logic is correct, the high pressure in the clutchcircuit (holding the clutch dis-engaged) is dumped, and the clutch isprogressively engaged.
So this is the function of the low pressure pump – to providea source of pressure to control the engagement of the clutch.
After September 1960 the low pressure pump was replaced by acentrifugal regulator, which serves the same purpose. It's worthwhilespeculating why Citroen decided to dump the pump. With any engineering changethere are always a number of reasons driving the change, maybe with a primaryreason. The combined pump is a fairly complex assembly which relies on threeface seals and a couple of O-rings to keep the fluids in place. The old adageis that oil and water dont mix, and having the two fluids in such closeproximity may have driven the change toseparate them. As we dont have any data on warranty claims from the time Iguess we can only speculate.
To be continued.
roger
You will never need to attend to one of these lovely little engineering pieces, but you may be interested in what is involved in bringing one back to life.
From it's launch in 1955 until September 1960, the DS19 wasfitted with a ingenious combined water pump and low pressure hydraulic pump.
The water pump was completely conventional and served todistribute coolant around the engine cooling circuit. However, co-axial withand in front of the water pump was a positive displacement hydraulic pump, bothpumps being driven at the same speed by a dual-belt drive.
The hydraulic pump is of the gerotor design (derived from “generated rotor”). The gerotor moduleconsists of an inner and outer rotor. The inner rotor has 4 teeth, and theouter rotor has 5 teeth. The outer rotor is located off-center and both rotorsrotate. The geometry of the two rotors partitions the volume between them intodifferent dynamically-changing volumes. During the assembly's rotation cycle,each of these volumes changes continuously, so any given volume first increases,and then decreases. An increase creates a vacuum which creates suction, andthis part of the cycle is where the intake is located. As a volume decreasescompression occurs. During this period hydraulic fluid under low pressure isdelivered to the hydraulic bloc (or “brain”).
Within the hydraulic bloc this pressure acts on a largediameter piston, and if the logic is correct, the high pressure in the clutchcircuit (holding the clutch dis-engaged) is dumped, and the clutch isprogressively engaged.
So this is the function of the low pressure pump – to providea source of pressure to control the engagement of the clutch.
After September 1960 the low pressure pump was replaced by acentrifugal regulator, which serves the same purpose. It's worthwhilespeculating why Citroen decided to dump the pump. With any engineering changethere are always a number of reasons driving the change, maybe with a primaryreason. The combined pump is a fairly complex assembly which relies on threeface seals and a couple of O-rings to keep the fluids in place. The old adageis that oil and water dont mix, and having the two fluids in such closeproximity may have driven the change toseparate them. As we dont have any data on warranty claims from the time Iguess we can only speculate.
To be continued.
roger