what's the use of the damper inline to the fuel pump?

[Mordan]

Hello!

My fuel pump is getting noisy and thinking about changing it. When looking at the details I see this item called "Damper". Is it a wearing part? thx!

Also I just noticed there is 2 different pumps!?! Fuel pump #5 and Suction device w.pump #6

http://bmwfans.info/parts/catalog/E34/Sedan/Europe/518i-M40/LHD/M/1990/september/browse/fuel_supply/sending_unit_assembly_plastic_fuel_tank/

[ss2115]

Hello!

My fuel pump is getting noisy and thinking about changing it. When looking at the details I see this item called "Damper". Is it a wearing part? thx!

Also I just noticed there is 2 different pumps!?! Fuel pump #5 and Suction device w.pump #6

http://bmwfans.info/parts/catalog/E34/Sedan/Europe/518i-M40/LHD/M/1990/september/browse/fuel_supply/sending_unit_assembly_plastic_fuel_tank/

The fuel pump immersed in the tank is low presure/high volume. It picks up the fuel from the bottom of the tank and delivers it to the next pump in the line (#5) which is a high pressure pump to bring the fuel pressure up to around 3 bar for the fuel injectors.
The higher volume of the immersed pump in the tank insurs that the high pressure pump doesn't run out of fuel.
Its much like a high pressure cleaner - the tap pressure delivers low pressure/high volume to the Gerni, and then the high pressure pump in the Gerni send the water out a much smaller diameter hose but at high pressure.

The damper is to help remove the surges of the immersed fuel pump as it takes big gulps of fuel and so the fuel between it and the high pressure pump surges each time the low pressure pump sends a vane full of fuel up the line.

I don't know the construction of the damper, but its most likely a rubber diaphram that expands on the inrush of fuel and releases on the inbetween strokes of the immersed fuel pump.
On this and its reliability, I'm sure someone else here could comment.

Hope this helps.

[mikell]

The early e30s had 2 pumps, but later ones just have one pump - make sure which one you have. The single pum bersions do not have the damper.

[Mordan]

The fuel pump immersed in the tank is low presure/high volume. It picks up the fuel from the bottom of the tank and delivers it to the next pump in the line (#5) which is a high pressure pump to bring the fuel pressure up to around 3 bar for the fuel injectors.
The higher volume of the immersed pump in the tank insurs that the high pressure pump doesn't run out of fuel.
Its much like a high pressure cleaner - the tap pressure delivers low pressure/high volume to the Gerni, and then the high pressure pump in the Gerni send the water out a much smaller diameter hose but at high pressure.

The damper is to help remove the surges of the immersed fuel pump as it takes big gulps of fuel and so the fuel between it and the high pressure pump surges each time the low pressure pump sends a vane full of fuel up the line.

I don't know the construction of the damper, but its most likely a rubber diaphram that expands on the inrush of fuel and releases on the inbetween strokes of the immersed fuel pump.
On this and its reliability, I'm sure someone else here could comment.

Hope this helps.

thx for the explanation which sounds good. at least I understand the damper now :). But I'm 90% sure my E34 has only 1 pump and one pressure regulator. My Haynes says so. Actually I'm asking because the ETK confuses me by giving me the choice between 2 kind of pumps to order.

http://bmwfans.info/parts/catalog/E34/Sedan/Europe/518i-M40/LHD/M/1990/september/browse/fuel_supply/sending_unit_assembly_metal_tank/

either
#5 16 14 1 181 354 http://bmwfans.info/parts/catalog/16141181354/
or
#6 16 14 7 161 387 http://bmwfans.info/parts/catalog/16147161387/

Mikell. I'm talking about my E34. My E30 which is the older model but already a motronic also has 1 pump. I'm pretty sure but not 100% certain since I haven't done the job on either cars. the reason why I'm asking.

PS: Euro spec car so beware.

[ss2115]

thx for the explanation which sounds good. at least I understand the damper now :). But I'm 90% sure my E34 has only 1 pump and one pressure regulator. My Haynes says so. Actually I'm asking because the ETK confuses me by giving me the choice between 2 kind of pumps to order.

http://bmwfans.info/parts/catalog/E34/Sedan/Europe/518i-M40/LHD/M/1990/september/browse/fuel_supply/sending_unit_assembly_metal_tank/

either
#5 16 14 1 181 354 http://bmwfans.info/parts/catalog/16141181354/
or
#6 16 14 7 161 387 http://bmwfans.info/parts/catalog/16147161387/

Mikell. I'm talking about my E34. My E30 which is the older model but already a motronic also has 1 pump. I'm pretty sure but not 100% certain since I haven't done the job on either cars. the reason why I'm asking.

PS: Euro spec car so beware.

As has been mentioned by someone else here, if you only have one pump, it will be in the tank as a combined pump/pickup unit and there won't be a damper.
It will be a high pressure pump and as it is a roller pump the pumping pulses are negligable and so the damper isn't required.