Racor pre-filter location

Oct 30, 2013
18
Wauquiez Gladiateur Anacortes
This may not be the right forum, but I have a fuel filter location question. The motor is an old but well running volvo md7b. I am going to upgrade and relocate the fuel pre-filter. Current setup is a completely (at least to me) inaccessible volvo prefilter and a standard screw on filter on the motor. I want to mount a new Racor prefilter in an accessible location. The prefilter appears to be gravity fed from the fuel tanks. Does it matter if I mount the prefilter further from the tanks, and higher than the tanks within the engine compartment so I can make them accessible? I assume the fuel pump will provide enough suction for the system.
 
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Sep 25, 2008
7,077
Alden 50 Sarasota, Florida
Elevating the primary filter might be convenient but brings the likelihood of unintended consequences such as sucking air into the fuel system.
 
Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
This may not be the right forum, but I have a fuel filter locationquestion. The motor is an old but well running volvo md7b. I am going to upgrade and relocate the fuel pre-filter. Current setup is a completely (at least to me) inaccessible volvo prefilter and a standard screw on filter on the motor. I want to mount a new Racor prefilter in an accessible location. The prefilter appears to be gravity fed from the fuel tanks. Does it matter if I mount the prefilter further from the tanks, and higher than the tanks within the engine compartment so I can make them accessible? I assume the fuel pump will provide enough suction for the system.

If you want to mount the filter above the level of the tank you'll want to ensure it has an anti-drainback / check-valve. Racor has them and mandates this in their installation instructions in order to "maintain prime"..
 
May 20, 2016
3,014
Catalina 36 MK1 94 Everett, WA
You will probably wan to add a lift pump if gravity is no longer your friend. The lift pump should go between the filter and the engine. 4-6psi and 15+ gal/hr.
 

Dan_Y

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Oct 13, 2008
514
Hunter 36 Hampton
If you want to mount the filter above the level of the tank you'll want to ensure it has an anti-drainback / check-valve. Racor has them and mandates this in their installation instructions in order to "maintain prime"..
Yard mounted a Raycor 500FG about 18 inches above tank in previous boat and because of the internal check ball and good lines/installation, it didn’t loose prime for the 5 years we had it. Just shut off the tank fuel valve when changing the element, though it probably doesn’t matter with that filter.
 
Aug 22, 2017
1,609
Hunter 26.5 West Palm Beach
You will probably wan to add a lift pump if gravity is no longer your friend. The lift pump should go between the filter and the engine. 4-6psi and 15+ gal/hr.
Why between the filter & the engine? I normally mount them between the tank & the filter. That way, when I change the filter, I can prime it with the pump.
 
May 20, 2016
3,014
Catalina 36 MK1 94 Everett, WA
Rancor specifies that as the prefered orientation. It still primed the filter just fine. If you use vacuum gauge to determine filter “fullness” they only work if the pump is after the Racor. I suspect you’ll have less leakage also.

Les
 
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Aug 22, 2017
1,609
Hunter 26.5 West Palm Beach
Thanks. Those are valid considerations. Apparently, your pump has better suction than mine. Mine would not draw fuel into an air bound filter.
 
Jun 1, 2007
265
O'Day 322 Mt.Sinai
Why between the filter & the engine? I normally mount them between the tank & the filter. That way, when I change the filter, I can prime it with the pump.
I added a 12VDC fuel pump as an aide to bleeding my 2GM20F, and also added a few valves so I can by-pass my engine and polish my fuel. The pump specified mounting a filter upstream of it to protect the pump, so I did. No issues pulling fuel into the 500FG filter.
 
Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
Why between the filter & the engine?
Because the primary filter, what you call the pre-filter, is supposed to do just that: filter. There is a small filter in the bottom of most fuel pumps, but it is NOT what you want and need as the first line of defense of filtration.
 
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Jun 11, 2004
1,621
Oday 31 Redondo Beach
Why between the filter & the engine? I normally mount them between the tank & the filter.

Because the primary filter, what you call the pre-filter, is supposed to do just that: filter. There is a small filter in the bottom of most fuel pumps, but it is NOT what you want and need as the first line of defense of filtration.
I thought it was because the pump might "emulsify" (for lack of a better term) any water in the fuel before it got to the filter and thus make the filter less effective at removing the water.
 
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Aug 22, 2017
1,609
Hunter 26.5 West Palm Beach
Why between the filter & the engine? I normally mount them between the tank & the filter.
...I thought it was because the pump might "emulsify" (for lack of a better term) any water in the fuel before it got to the filter and thus make the filter less effective at removing the water.
Emulsify is the correct term. I had not considered that possibility. I also don't know the minimum droplet size that the water blocking filters can stop.

In practice, I have not had any issues with any of the systems I have set up with the pump before the filter, but depending on what type of pump was used, I suppose that in some cases emulsification could be an issue.
 
Aug 22, 2017
1,609
Hunter 26.5 West Palm Beach
Because the primary filter, what you call the pre-filter, is supposed to do just that: filter. There is a small filter in the bottom of most fuel pumps, but it is NOT what you want and need as the first line of defense of filtration.
I guess that you are protecting from a situation in which the crud in the tank is big enough to jam up the pump. I haven't had that situation yet, but I can see where it could happen.

After reading all of this, it appears to me that the following is a summation -

Putting the pump before the filter has the advantage of allowing you to power prime the filter after a filter change, but runs the risk of emulsifying water into the fuel & helping the water to maybe get past the filter, depending on the type of filter & pump.

Putting the pump after the filter, but before the motor, protects the pump from debris in the intake line, but runs the risk of an airbound filter preventing the pump from getting a prime & working.

In the past, with the pump after the filter, I have needed to pour fuel into the filter housing when I change the filter, otherwise the pump would not work. That is why I chose to put my pump first. I now see that there are risks involved that I had not considered.
 
May 20, 2016
3,014
Catalina 36 MK1 94 Everett, WA
Or all of you who use priming as s reason to put the pump between the tank and filter, have you tried it the other way?? These lift pumps have really good suction, I’ve bench tested both cheap turbine and expensive facet lift pumps at over 4’ of suction and the pumps could fill the Racor.

If your having problems you probably have a air leak which would be a fuel leak with the pump the other way

The reason I put the pump in between the Racor and the engine is because that’s what the installation instructions say to do. They have smart engineers that I trust. Plus I can use vacuum gauge to tell me when I need a filter change.

Les
 
Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
Racor wants to see the pump on the suction side for the best filter performance. I have never seen a good quality pump that could not prime a Racor filter from the suction side..
 
Aug 22, 2017
1,609
Hunter 26.5 West Palm Beach
I am using the clear view filters. Those are required to be above deck by regulation. If my filter was lower in the boat, I would probably not have the issue with priming.
 
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
@JimInPB Les's point about air infiltration is a good point. Perhaps the issue is the pump. Check out the spec's on this one.
http://walbrofuelpumps.com/frb-11.html
  • Self-Priming (Dry Lift) of more than 48" (120 cm)
  • Continuous Duty Life Over 18,000 Hours (Diesel Fuel)
  • Dry Run to Four Hours
  • Low Current Draw
 
Nov 14, 2013
200
Catalina 50 Seattle
Regarding water in the fuel, Racor filters are hydrophobic and will not absorb or pass water droplets larger than their nominal pore size. As long as the water is not dissolved in the fuel and, if emulsified, the water droplets are bigger than 2/10/30 microns (pick your filter), it won't get through. A diaphragm pump simple can't emulsify water to that degree. You'd need a high speed gear or impeller pump and even then, it's tough to get a droplet size in the 10um range so it can pass through the filter.
Note that some fuel filters are designed with a hydrophillic medium to absorb dissolved and/or highly emulsified water but the Racor filters for the common turbine units aren't that design.
 
Jun 11, 2004
1,621
Oday 31 Redondo Beach
Regarding water in the fuel, Racor filters are hydrophobic and will not absorb or pass water droplets larger than their nominal pore size. As long as the water is not dissolved in the fuel and, if emulsified, the water droplets are bigger than 2/10/30 microns (pick your filter), it won't get through. A diaphragm pump simple can't emulsify water to that degree. You'd need a high speed gear or impeller pump and even then, it's tough to get a droplet size in the 10um range so it can pass through the filter.
Note that some fuel filters are designed with a hydrophillic medium to absorb dissolved and/or highly emulsified water but the Racor filters for the common turbine units aren't that design.
Whatever, but Racor says this.
"Pressure Side: ... Not ideal - pumps emulsify water hindering filter performance."