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     Marc Hughston Moderator Username: Hughston Post Number: 388 Registered: 03-2003 |
The attachment at the link below is a pdf of the handout for class tonight. Included are instructions for bleeding and priming the Westerbeke 40 on Pilgrimage, and several pages from Nigel Calder's "Marin Diesel Engines" which discusses general procedures for bleeding a diesel fuel system.
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| Marc Hughston Moderator Username: Hughston Post Number: 386 Registered: 03-2003 |
David Sheriff led me through this procedure on Pilgrimage at Santa Barbara Island in 2002 when air got into the fuel line. What I remembered was enough to help me in 2005 on Lucinda Mae when we ran out of fuel on the way back from Catalina, even though it was a very different engine. My search in this topic is for the key issues and steps that have to take place in order to restart the engine after filters are changed or after running out of fuel. My objective is to find the common general procedures that can be made specific enough to be of real value on different engines. My research so far has involved reading the relevant sections of manual for the Westerbeke 40 on board Pilgrimage, including some handwritten notes from 1993 and poking around the engine to identify lines, filters, pumps and bleed screws; looking for the same stuff on Half Moon’s Yanmar 2GM20F, and La Mouette’s Volvo MD7A; searching the web – not much there; reading the relevant sections of Nigel Calder’s “Marine Diesel Engines – Maintenance, Troubleshooting, and Repair.” The book is good. I’m going to start carrying it with me on voyages. Here’s a summary of the info that I think makes a difference, and the general procedures that can be used on different engines. I’ll have more specifics and handouts at Monday’s class. Why would you need to bleed the fuel system? Air has been introduced into the fuel lines, and the engine will not run as a result. Basically, fuel has to get from the tank to the injectors which deliver it to the combustion chamber in each cylinder, and if there is air in a line somewhere in between, fuel delivery is interrupted (this doesn’t happen on a gas engine, just on a diesel). Bleeding the system means pumping the fuel through the lines to a bleed screw or connection which can be slackened to let the air escape. How does air get in to the fuel lines? The most common causes include changing the fuel filters, and running out of fuel or getting low on fuel so that air is sucked into the line. There are other possible causes – see Calder’s book. How do you bleed the line? The overall approach is this: pump fuel through the line to a bleed screw, nipple, or fuel line connection which, when slackened, allows the air to escape. There will be bubbling fuel escaping, and when the bubbles stop and fuel streams continuously, the air is gone – tighten the nut back down. When filters are changed, you may get away with just bleeding the line leading from the filter. When you run out of fuel, you’ll have to bleed the whole system up to the injectors. Rubber gloves will protect your hands, and absorbent diapers are a must to keep fuel from getting into the bilge and being discharged overboard. How do you pump the fuel? Many primary fuel filters like the Racors on Pilgrimage and Half Moon have a pump built right into them on the top of the filter housing. The low pressure lift pump mounted on the engine that draws fuel from the tank through the primary filter and on to the secondary filter will often have a manual lever you operate by hand. The high-pressure injection pump is operated by cranking the engine. Where do you bleed the lines? At almost every step from primary filter to injector, there will be a screw or nut on the filter housing or pump body or a fuel line connection that can be loosened to let air escape. Fuel moves from the tank to the injectors, so start closest to the tank with the primary filter if you’ve run out of fuel, or with the filter you just changed, then work forward in the system to the injectors. Likely spots to bleed the lines, going from the tank to the injectors: Primary fuel filter - bleed screw or hose connection going out to lift pump. Secondary fuel filter - bleed screw or hose connection going out to injection pump Injection pump - a.) fuel inlet connection from secondary filter b.) bleed screw or outlet connection. Injectors – each has a nut where the the high-pressure line leading from the injection pump connects to it, and that nut at the injector can be backed off to allow air to escape. Background on the system components: Generally, there is a low-pressure component and a high-pressure component to the fuel system. The low pressure system includes 1) the primary filter between the fuel tank and lift pump – this is the one that has the water separator and sediment bowl; 2) the final or secondary filter between the lift pump and the high pressure injection pump; 3) the connection of the line from the secondary filter to the injection pump. The High-pressure system includes the injection pump and the lines leading from it to the injectors. I’ll have more for you Monday evening including diagrams of the fuel system, and my objective will be to identify all the parts on Half Moon and go through the procedure. For anyone monitoring this subject, how helpful is this so far? |
handout