There has been discussion about pusher pumps lately for our diesel rigs. I am looking at putting one on a truck, and started researching. I found the following information, and wonder if anyone else has read the same, talked with any Walbo techs, or practices what is being recommeded (filter in front of the pusher pump).
I do understand the current generation of Walbro filters do have a filter built in, on the inlet side, and wonder if this is simply dated information.
Here is a link to the 6000 series pumps:
http://www.autoperformanceengineering.com/html/6000_pump.html The diesel pump has a 420 micron filter, which as quite large. Indicates to me one would be fine putting the filters after the pump, as the pump would be built to handle anything under that size with no damage.
This is pulled of a Sami Diesel list.
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QUOTE
There has been some interest on the list in using a diesel fuel pump to prime the fuel system after changing filters. One suggestion has been to use the pump in a "flow thorough" configuration. The general fuel flow scheme was from tank to pump to filters to engine. In this arrangement, the pump would not run except when filling the filters or in emergency conditions. This concept requires that the fuel flows through the pump
with little pressure drop when its motor isn't running.
The notion of pulling unfiltered fuel through a non-running pump bothered me, but I had no data to support my concern. The pump generally thought of in this configuration is made by Walbro. To get to the heart of the matter, I had a long discussion with the Walbro Engineering Department. The results of that discussion are listed below:
PUMP FACTS
1. The Walbro pump is intended for continuous service and its service life should exceed 10,000 hours. It contains an inlet and an outlet valve. The valves are opened and closed by the action of a piston moving up and down in a cylinder in the motor. The valves are kept closed by springs. Other than the valves, springs, and piston, there are no moving parts in the pump. All in all, it is a very well made and long lasting pump.
2. If fuel flows through the pump while the pump motor is not operating, there will be a pressure drop across the pump caused by the energy necessary to keep the valves open. The pump IS NOT approved for such operation. Since it is not approved for such operation, the pressure drop across the pump has not been measured in that mode. It is expected that the pressure drop when operating in that mode will be different at different times in a random fashion by any number of factors which could affect the position of the valves.
3. Any debris getting under either valve would cause the pump to stop pumping any fuel at all. To protect against this problem, a 30-micron screen is installed in the inlet of the pump. In the marine pump, it can only be cleaned by partially taking the pump apart. Any debris caught by the screen will increase the vacuum across the pump (and system if the pump is not running). Note that the 30-micron screen is the same micron level as used in many Racor filters. Any debris passing the screen can cause the valves not to work and might damage them. The pump IS NOT approved to operate without a filter on its inlet side. If the pump is operated without such a filter, the WARRANTY IS VOIDED.
______________________________________________
CONCLUSIONS
1. Protecting the pump with a filter is mandated by this pump manufacturer, but it is often necessary, and generally good practice, to protect any pump with a filter on its inlet side. Not protecting any pump in this way should be done only with great care.
2. The Walbro pump can still be used to prime filters when it is installed on the engine side of the filter(s).
3. Unless the pump is used as a fuel pump all the time, it should have a bypass around it so that fuel will not flow through the pump when the pump is not running.
4. Unless the bypass around the injection pump can't handle the 7-psi maximum pressure of the Walbro, there is no reason that it can't runcontinuously as a fuel pump in cooperation with the normal engine-mounted lift pump. In this configuration, a bypass around the Walbro could still be of benefit.
____________________________________________________
From the conclusions, you can see that there are many configurations possible in the diesel piping. The object is to make sure that the installed piping really does what you want it to do. One of the most important factors in doing that is to get the requirements of the equipment from the manufacturer.
END QUOTE
I do understand the current generation of Walbro filters do have a filter built in, on the inlet side, and wonder if this is simply dated information.
Here is a link to the 6000 series pumps:
http://www.autoperformanceengineering.com/html/6000_pump.html The diesel pump has a 420 micron filter, which as quite large. Indicates to me one would be fine putting the filters after the pump, as the pump would be built to handle anything under that size with no damage.
This is pulled of a Sami Diesel list.
gb
+++++++++++++
QUOTE
There has been some interest on the list in using a diesel fuel pump to prime the fuel system after changing filters. One suggestion has been to use the pump in a "flow thorough" configuration. The general fuel flow scheme was from tank to pump to filters to engine. In this arrangement, the pump would not run except when filling the filters or in emergency conditions. This concept requires that the fuel flows through the pump
with little pressure drop when its motor isn't running.
The notion of pulling unfiltered fuel through a non-running pump bothered me, but I had no data to support my concern. The pump generally thought of in this configuration is made by Walbro. To get to the heart of the matter, I had a long discussion with the Walbro Engineering Department. The results of that discussion are listed below:
PUMP FACTS
1. The Walbro pump is intended for continuous service and its service life should exceed 10,000 hours. It contains an inlet and an outlet valve. The valves are opened and closed by the action of a piston moving up and down in a cylinder in the motor. The valves are kept closed by springs. Other than the valves, springs, and piston, there are no moving parts in the pump. All in all, it is a very well made and long lasting pump.
2. If fuel flows through the pump while the pump motor is not operating, there will be a pressure drop across the pump caused by the energy necessary to keep the valves open. The pump IS NOT approved for such operation. Since it is not approved for such operation, the pressure drop across the pump has not been measured in that mode. It is expected that the pressure drop when operating in that mode will be different at different times in a random fashion by any number of factors which could affect the position of the valves.
3. Any debris getting under either valve would cause the pump to stop pumping any fuel at all. To protect against this problem, a 30-micron screen is installed in the inlet of the pump. In the marine pump, it can only be cleaned by partially taking the pump apart. Any debris caught by the screen will increase the vacuum across the pump (and system if the pump is not running). Note that the 30-micron screen is the same micron level as used in many Racor filters. Any debris passing the screen can cause the valves not to work and might damage them. The pump IS NOT approved to operate without a filter on its inlet side. If the pump is operated without such a filter, the WARRANTY IS VOIDED.
______________________________________________
CONCLUSIONS
1. Protecting the pump with a filter is mandated by this pump manufacturer, but it is often necessary, and generally good practice, to protect any pump with a filter on its inlet side. Not protecting any pump in this way should be done only with great care.
2. The Walbro pump can still be used to prime filters when it is installed on the engine side of the filter(s).
3. Unless the pump is used as a fuel pump all the time, it should have a bypass around it so that fuel will not flow through the pump when the pump is not running.
4. Unless the bypass around the injection pump can't handle the 7-psi maximum pressure of the Walbro, there is no reason that it can't runcontinuously as a fuel pump in cooperation with the normal engine-mounted lift pump. In this configuration, a bypass around the Walbro could still be of benefit.
____________________________________________________
From the conclusions, you can see that there are many configurations possible in the diesel piping. The object is to make sure that the installed piping really does what you want it to do. One of the most important factors in doing that is to get the requirements of the equipment from the manufacturer.
END QUOTE
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