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Author Topic: Fuel line vacuum gauge  (Read 326 times)

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John Langford

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Fuel line vacuum gauge
« on: January 24, 2019, 04:45:14 PM »

Inspired by a Cruising World piece, I recently installed an oil filled Durachoice 0-30 inHg vacuum gauge between my primary Racor filter and my fuel pump. I installed it vertically against the wooden frame for the engine compartment on the starboard side with gauge facing forward. It can be read by lifting the companionway access hatch under the upper set of steps. The installation was straightforward and the engine works fine. So fuel supply is fine. The odd thing is that there is no deflection of the gauge when the engine is running. I have recently changed filters so I wouldn’t expect much deflection. But none?

Any thoughts?

The Cruising World article can be found at: https://www.cruisingworld.com/how/fuel-filter-gauge
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Gregory M

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Re: Fuel line vacuum gauge
« Reply #1 on: January 24, 2019, 08:23:03 PM »

"None" is good! Vaccum gauge will operate, if filter is plugging up. Zero vaccum=full flow. Check with high rpm (full throttle). After changing my fuel tank and all fuel lines it took  all summer to move just a bit. When it goes to about "-20", is time to change filter.
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Gregory, "Luna Rossa", #1063, 1990, Mk 1.5, fin keel. Universal M 35,  Rocna 15,
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KWKloeber

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Re: Fuel line vacuum gauge
« Reply #2 on: January 24, 2019, 09:57:50 PM »

I have recently changed filters so I wouldn’t expect much deflection. But none?

Any thoughts?

The Cruising World article can be found at: https://www.cruisingworld.com/how/fuel-filter-gauge

You need to read it at high RPM, when are you reading it?  A dragging needle gauge is typically used where it's not easily read at open throttle. 
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Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
So throw off the bowlines.  Sail away from the safe harbor.  Catch the tradewinds in your sails.
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mainesail

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Re: Fuel line vacuum gauge
« Reply #3 on: January 25, 2019, 05:35:47 AM »

  A dragging needle gauge is typically used where it's not easily read at open throttle.

As Ken mentioned, drag needle gauges are much preferred as you can look at them any time and see max vacuum. Also the vacuum gauge needs to be installed in the correct location and that is after or physically measuring the resistance in the primary filter.
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John Langford

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Re: Fuel line vacuum gauge
« Reply #4 on: January 26, 2019, 04:50:28 PM »

Thanks to all. A drag needle would have been good. I sail mostly alone so leaving the helm, removing the steps and lifting the companionway engine hatch for a look while running at 2200 rpm isn’t without its challenges. So far I have only checked it at the dock running at 1500rpm.
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Breakin Away

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Re: Fuel line vacuum gauge
« Reply #5 on: January 26, 2019, 09:19:36 PM »

Hi all,

I'd love to put a vacuum gauge on my Racor, but I have a 215R spin-on type due to space limitations. It does seem like there are a couple of possible ports right on the housing downstream of the filter: only one of the two 1/4"-18 NPT outlet ports is used for the fuel line, so I could pull the plug out of the second one and screw in a vacuum gauge on that. Also, there is a 3/8"-24 SAE vent plug on the top that might be used. Any suggestions between these two?

Also, does the gauge need to be oriented vertically, or can it be "lying flat" after screwing directly into the outlet port? (Adding an elbow would be easy in theory, but there's not enough vertical clearance to have the gauge in a vertical orientation.)

I've attached a schematic of Racor's 2xxR series. Note also that it includes a pressure drop graph for the clean filter, but at my typical consumption rate of about 0.6 GPH, it's effectively zero. Any idea what the pressure drop is when the filter is on the verge of clogging? (I guess this would correspond pretty close to the suction limit of the lift pump.)
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KWKloeber

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Re: Fuel line vacuum gauge
« Reply #6 on: January 26, 2019, 11:33:59 PM »

ba-

The gauge needs to read the suction somewhere between the filter --> lift pump.  So if space is limited it could be put in-line between the two, or mounted elsewhere with the fuel hose run to it and back to the pump.

Yes, the gauge can be any orientation, in your case flat or sideways or angled the easiest to read is ok.

The B series have a Kubota pump so I don't know the lift -- but if it's, say 36", that would be only about 3" vacuum.  Far from the 10" danger point on the Racor gauge below (so obviously that gauge is good for much higher flow and more powerful pump as might be on industrial equipment.)  10" vacuum would be like 130" of suction lift.  The most powerful Facet cube pump is good for 96" lift, but most are 24"-36" lift. 

-k
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Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
So throw off the bowlines.  Sail away from the safe harbor.  Catch the tradewinds in your sails.
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Bobg

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Re: Fuel line vacuum gauge
« Reply #7 on: January 27, 2019, 11:34:04 AM »

Those dragging needle vacuum gauges are kinda hard to find on the web,well,inexpensive ones anyway..without the dragging needle you find them everywhere for around ten bucks but with the needle they soar to around 70 dollars (my search anyway)..anyone have a source for a decent price.? Like 25-30?
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John Langford

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Re: Fuel line vacuum gauge
« Reply #8 on: January 27, 2019, 11:43:04 AM »

One further thought on orientation of the gauge. If you use an oil-filled Durachoice gauge then vertical orientation allows you to rezero the gauge by pulling out the plunger without losing oil. Any other orientation would make adjusting the gauge problematic I believe.  BTW, I chose the oil filled gauge because it helps steady the action of the gauge if it is subject to vibration. Since I ended up installing it to the wall of engine box it shouldn’t be vibrating along with the engine. So perhaps I could have chosen a gauge model that wasn’t oil filled.
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KWKloeber

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Re: Fuel line vacuum gauge
« Reply #9 on: January 27, 2019, 01:58:27 PM »

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Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
So throw off the bowlines.  Sail away from the safe harbor.  Catch the tradewinds in your sails.
Explore.  Dream.  Discover.   -Mark Twain

Gregory M

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Re: Fuel line vacuum gauge
« Reply #10 on: January 27, 2019, 02:10:44 PM »

Sorry, to bump in to conversation, but why would we need drag needle? I'm assuming, that where would be the highest vac created?
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Gregory, "Luna Rossa", #1063, 1990, Mk 1.5, fin keel. Universal M 35,  Rocna 15,
Penetanguishene ON.

KWKloeber

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Re: Fuel line vacuum gauge
« Reply #11 on: January 27, 2019, 02:22:41 PM »

Sorry, to bump in to conversation, but why would we need drag needle? I'm assuming, that where would be the highest vac created?


Just read down the topic!
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Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
So throw off the bowlines.  Sail away from the safe harbor.  Catch the tradewinds in your sails.
Explore.  Dream.  Discover.   -Mark Twain

KWKloeber

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Re: Fuel line vacuum gauge
« Reply #12 on: January 27, 2019, 02:56:54 PM »

Quote from: KWKloeber

or mounted elsewhere with the fuel hose run to it and back to the pump.


D’oh.  Or ( easier) tee’d in to the suction anywhere (filter port, hose) and a single line run to the gauge mounted elsewhere.

-k
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Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
So throw off the bowlines.  Sail away from the safe harbor.  Catch the tradewinds in your sails.
Explore.  Dream.  Discover.   -Mark Twain

Breakin Away

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Re: Fuel line vacuum gauge
« Reply #13 on: January 27, 2019, 03:20:09 PM »

Sorry, to bump in to conversation, but why would we need drag needle? I'm assuming, that where would be the highest vac created?
Here's the scenario I envision: You're out there on the water and your motor suddenly dies. (Been there, done that.) Why? Is it an air leak or pocket on the fuel system, is it a clogged secondary filter, is it a clogged primary filter? A vacuum gauge can determine whether it's the latter, but only if the engine is running. What if you can't get the engine running again? That would prevent you from seeing the vacuum reading. A drag needle will let you know whether you should first replace your primary filter even if your motor won't start.

A couple of other points of clarification:

My 215R is a very poor design for a couple of reasons. You can't pull the filter up and out to inspect it - the filter is on the bottom, which can't be inspected and is a mess to clean up. Also, the spin-on filters are much more expensive. (Only real benefit of 215R is low profile design for confined spaces.) For both of these reasons, having a vacuum gauge would be very helpful, because it can save a lot of money on potentially unnecessary filter changes, since it can't be checked any other way. In fact, with a vacuum gauge I'd be tempted to let my current filter run to the point of clogging just to see what the vacuum level is, then I'd know to replace the next filter when the vacuum gets to 80% of the clog point.

Also, my interest in putting it right on the filter housing is because I prefer NOT to install it on any of the cabinetry. I've removed the aft berth motor box to do transmission and HX work before, and would like to continue to do so without having to remember to remove the vacuum gauge first (or, if I forget, do some major damage that could create a diesel fuel mess). I realize that there are other possible places to mount the gauge, and I will survey the boat for such locations next time I'm there, but wooden cabinetry is off-limits AFAIC.
« Last Edit: January 27, 2019, 05:06:54 PM by Breakin Away »
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Noah

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Re: Fuel line vacuum gauge
« Reply #14 on: January 27, 2019, 04:26:48 PM »

This is my set up on a MKI. MKIIs may have different access. The Racor 500 turbine cost approx $215 and the vacuum gauge was $90. Not cheap but works properly. The other gadget is my Balmer 614 voltage regulator.
« Last Edit: January 27, 2019, 04:28:19 PM by Noah »
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