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Old 01-03-2010, 13:31   #1
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How Is a Diesel LP Fuel Pump Regulated?

I was wondering how a diesel LP fuel pump works. I have a Perkin 4.236. What could be used as backup replacement. Is the pump on at all times while the engine is running.? How many gallons per hour would the engine pump?

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Old 01-03-2010, 13:44   #2
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A popular fuel pump in the UK is an SU.
Its a diaphram type actuated by electro magnet which is switched by a set of points like in a distributor and is self switched by a pressure switch.
Uses so little current, its quiet and only runs when needed but fuel lines must be in good order with no leaks.

http://www.sucarb.co.uk/
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Old 01-03-2010, 14:03   #3
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Any electric fuel pump will work, with a few exceptions. I am not familar with the exact engine, but some engines require a certain volume of fuel to be circulated back to the tank, while others just need fuel fed to the injection pump at a relativly low pressure. Either way, just about any pump will work, some of the most common are like Anjou describes, just simple electric diaphram pumps. I've put several facet pumps on older engines that the lift pumps became impractical to repair or replace.
http://www.aircraftspruce.com/menus/...telectric.html
these are some of what I've used
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Old 01-03-2010, 15:11   #4
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Mine runs all the time...I have no mechanical pump on the engine....I have a 4-154....very similar to your 4-236...

As far as backup and the sort...They also make bleeding the primary fuel system simpler....mine is a little noisy....way down on the list right now though.

Unlike a cars carburetor Diesels constantly bypass extra fuel so the pumps do not pressure up and stop.
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Old 01-03-2010, 15:21   #5
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I found Pegasus Racing as a source:
Pegasus - Facet Electric Fuel Pumps & Accessories

I've only set up one side, but evenually will have parallet RACORs and pumps at the tank with swich and valves to for quick changeover.
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Old 01-03-2010, 16:45   #6
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There are many type of lift pumps out there but they really fall into two categories, mechanical and electric. Speaking generally, mechanical pumps tend to be more trouble free. They are usually driven off the cam but some are belt driven. Most mechanical pumps have a diaphragm and two check valves although some are impeller type. Electric pumps can work quite well and do make bleeding the system easier.

When specifying a pump that is different than the stock one, pressure and flow rate are important as well as durability since the pump runs continuously whenever the engine is on. The end goal is to get adequate fuel flow to the injection pump at the correct pressure. Your injection pump will have an overflow valve which is a spring loaded valve that controls how much fuel flows back to the tank which also regulates pressure. Typically, an engine will return ~90% of the fuel to the tank so you can get an idea of the volume required. If the pressure at the IP is too low, you will have low power and may actually damage your injection pump depending on how it is lubricated. Overflow valves are not perfect regulators so if the flow to the pump is great enough, too high of pressure is possible too. Too much pressure is an issue as well since it will damage certain parts inside the injection pump.

If you are going to an aftermarket electric pump, look at getting a good one. If you buy a cheap pump, you will end up having to replace it and likely an IP at some point as well. In addition, the nicer pumps let you regulate the pressure at the pump. I would highly suggest the pumps made by FASS (even their smallest one would be plenty for the given engine) and you can get the pressure right. I don't know what the fuel pressure spec is for the given engine off the top of my head but it shouldn't be hard to find. You don't need the pressure to be exact but you should be in the given range at all rpms and loads.
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Old 01-03-2010, 20:50   #7
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Not much ..about 8 psi
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