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Old 07-02-2012, 11:17 PM   #1
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A small amount of air in a Perkins fuel lines.

Need your opinion. I need to replace the petcocks in the bottom of the Racor fuel filter/water separators. They are seeping slightly. I have new parts. I know I will drain the filter fuel contents as well as fuel from the in and out fuel lines in the process. I carry a gallon of diesel to refill the filters when I change elements. This takes care of most but not all the air I let in. There will still be air in the lines between the tanks and the filters and the filters and the distrubution manifolds (not much volume) when I refill the filters.

Question? Do I have to worry about the air or will it purge itself in the fuel pump and return lines? I know the engines return far more fuel than they burn, so I am guessing Iím OK. What do you think?
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Old 07-03-2012, 12:40 AM   #2
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If the engines are primed when they are shut down,meaning there is no air in the injection pump or lines to the injectors,you should be OK just filling the filters up.The fuel flowing from the filters to the injection pump should pull fuel from the tanks.Make sure the tank vents are clear and not clogged or partially clogged.I remove the fuel cap on first start up but I am just paranoid about vent lines.
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Old 07-03-2012, 12:53 AM   #3
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As long as you don't break the lines between your secondary filter (on top of the engine) and the CAV injector pump you should be fine. The only time I have to bleed the injection system is when I replace that secondary filter and then you have to go through the whole bleeding routine right up to the injectors.

I take it the primary filter you are concerned with is between the tanks and engine fuel lift pump? If so you shouldn't get much bleed back. I have a fuel shutoff valve on the inlet side of that filter to stop flow from the tanks. Makes life a lot easier when changing that filter out.
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Old 07-03-2012, 06:18 AM   #4
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I know the engines return far more fuel than they burn, so I am guessing I’m OK.


SOME engines return vast amounts of fuel.

Mostly Detroit Diesels.

Marinizations with "Bosch Style" injection (high pressure pump and steel lines to injectors at hat run at 1800PSI)will return only minor fuel.

Mostly just what leaks internally inside the injection pump.

Better to learn at dockside how to prime your system than underway.

Running out of fuel in a tank is a hassle , not a disaster .

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Old 07-03-2012, 07:33 AM   #5
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Is there a way to pinch down on the line to slow or stop air from getting in while you replace the drain valve? Maybe fill the line by hand with a mustard squirter up to the lift pump?

It's been a long time since I had to bleed Dr. Perky even after a secondary filter change.

I suppose without seeing your setup, it's hard to understand how you could prevent or fix the air in the line, BUT once you fix your filter, just bleed the line above the CAV secondary filter using the lift pump and you should be fine.

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Old 07-03-2012, 10:28 AM   #6
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What do you think?
Shut the valves that isolate the filter.

Open the top of the filter.

Drain bowl.

Replace drain valves.

Refill bowl.

Replace filter top.

Open isolation valves.

Start engine and idle for a few minutes while you drink a beer and pat yourself on the back.

(The few minutes running is just to reassure you that any stray air is not going to shutdown the engine.)

Gratuitous bleeding of high pressure lines inevitably leads to damaged fittings that create leaks and needless expense.
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Old 07-03-2012, 10:31 PM   #7
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Craig, We had a Perkins for years and if MOST of the air is out of the system, you should be able to start the engines and the Perkins will purge the rest of the air on its own. Just keep the throttle open until it runs smooth. Only takes a minute or so. We never had to bleed the engine when changing filter, Just filled the filters and fired it up. If you close the fuel valve on the tank, you won't loose all of the fuel in the lines. Don't forget to re-open it. Chuck
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Old 07-04-2012, 07:14 AM   #8
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Done Deal. refilled the filters after the petcock change and fired it up. No problem. Was interesting to watch the filters after the change. boat has off road diesel in it, and my refill diesel was on road. as the engines idled, you could see how the flow worked within the filter bowls as they changed from yellow/clear to red. Much slower flow than I would have guessed.
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Old 07-04-2012, 09:36 AM   #9
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Much slower flow than I would have guessed.
Try and spend an hour pouring a gallon of fuel out of a container
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Old 07-04-2012, 07:18 PM   #10
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Done Deal. refilled the filters after the petcock change and fired it up. No problem. Was interesting to watch the filters after the change. boat has off road diesel in it, and my refill diesel was on road. as the engines idled, you could see how the flow worked within the filter bowls as they changed from yellow/clear to red. Much slower flow than I would have guessed.
---------------------------------
Yeah, that primary filter is a piece of cake and I have done it several times while underway. (Another advantage of two engines.)

Do your fuel tanks sit higher than the filter and free flow fuel or do you have to pump it to the primary filter? Mine free flow when you open the filter up, consequently I added a small brass ball valve to the inlet side of the primary filter to shut the fuel flow off. Otherwise it was always a mess to change without shutting the fuel valves at the tanks.

Now the secondary filter is another story!!

Larry B
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Old 07-04-2012, 11:10 PM   #11
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My filters sit at about mid point vertically compared to the tanks. They will siphon if the tanks are full. That has made my nervous as the plastic petcocks were stripped and coudn't be closed beyond a very loose finger tight. I was always afraid vibration would open them. there are valves at the exits at the top of the tanks. I thought about adding valves at the inlet and outlet of the filters, as the hoses do drain and don't refill when the filter is filled. But I calculated the total volume as 5 cu. in. As it turns out, that is no problem at all. Last year I never had the tanks beyond half full after I realized the problem, so that all they could do is drain themselves. Never did but they were always slightly wet to the touch. I was surprised that after visiting 4 major truck/ diesel service and parts stores that nobody had Racor parts. Bought them off the internet. They are priced as if they are made of gold. $75 for two. They are a two piece plastic with a couple O rings. couldn't cost more than a few bucks to make. O well at least they are fixed.
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