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Separ SWK-2000-18 with vacuum gauge: what to expect?

Discussion in 'Engines' started by mapism, Jun 20, 2020.

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  1. mapism

    mapism Senior Member

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    I am going to replace the covers of some Separ filters with the one below, that includes a vacuum gauge for early spotting of progressive clogging in the filter cartridge.

    But those vacuum gauges are very rare to in European boats (not only for Separs BTW, but also Racors), while I can remember to have seen them in several installations in the US.

    So, I was wondering if someone can give me an idea of what I should expect to see as "normal" reading.
    I mean, in principle I would expect a reading very close to zero with clean new filters, and progressively increasing as the filter gets dirty.
    But I don't know what sort of PSI (if any) should be expected with clean new filters, and at which vacuum level it would be recommendable to replace the filters, so any suggestions/experiences would be appreciated.

    Just in case it matters, the engines burn 45 GPH @ WOT each, so the filters are way oversized, considering their rating of 285 GPH max.
    I suppose that could contribute to make any reading differences less noticeable, but again, no idea about what numbers to expect...

    Thanks in advance!

    [​IMG]
  2. Fishtigua

    Fishtigua Senior Member

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  3. d_meister

    d_meister Senior Member

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    Can't quite read the scale, but is that a dual range gauge with vacuum and pressure?
    If it is intended to read vacuum, the reading at almost any throttle position should be rather steady if the filters are not too fine, like 2 micron Racors, and new and clean. The initial reading will depend on if the fuel level is higher than the filter assembly, like a bulkhead tank, or lower, like a bilge tank. If there are bilge tanks, you may have as much as 4" of suction as a base point. If a bulkhead tank, there could be positive pressure at rest (1-2 psi), and a zero vacuum reading while running. Racor gauges (by Parker-Hannifin) show the peril zone to begin at 7" of vacuum and the no-go zone above 10".
    Ultimately, like Fish says, you'll find your set points from practise. Cut a wedge pointer from electrical tape and stick it on where it runs at normal throttle with full-ish tanks and clean filters.
    I've tried to have "suction" gauges on primary filters on any vessel for long deliveries. If I'm running lower RPM's (1200 +/-), I'll run 2 micron Racors. It beats changing secondarys when it is least convenient, as many secondary filters are 4 micron.
  4. Capt J

    Capt J Senior Member

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    I run 10 micron primaries, I've seen 3 newish boats where the 30 micron racors looked near perfect and the secondaries were plugged to the fact that the engine computers were alarming on low fuel pressure. Every boat is different, find them with use, run the boat at cruise for 30 minutes and see what they're at with fresh filters. Just because your engines consume 45 gph at cruise, the fuel pumps are still moving considerably more fuel than that through the filters, so the filters are not grossly oversized as you imagine. Generally I see 5-10 psi of vaccuum on the gauges at cruise speed.......10 psi more than whatever they run at with fresh filters (or 20 psi total) I'd change the filters.
  5. mapism

    mapism Senior Member

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    Doh! Thanks for the link, I actually bought the gauges from the Separ distributor in the US, and didn't think to check their UK website.

    But there is a statement in those instructions which I'm not sure to understand:
    "There is a small cap on the top of the gauge. When supplied a certain amount of air will be present inside the gauge; this should be expelled by the temporary removal of this cap. With the air bubble gone, the normally damped operation of this gauge can commence."

    Now, here's how the top of the gauge looks like:
    [​IMG]
    So, I assume that by "temporary removal of the cap" what they actually mean is a rotation of the yellow clip towards the open position.
    But should I keep it open with the engine running, till the air bubble is gone, and then close it again?

    @d_meister:
    the following pic shows you the scale better, but why do you think the position at rest should be relevant?
    I mean, I understand that the static position can be affected by the tank position, and also by how full they are, but for the intended purpose of the gauge, its reading is only relevant while fuel is circulating, "sucked" by the engine fuel pump and possibly restricted by a clogged filter.
    So, the position at rest should be irrelevant - or am I missing something?
    [​IMG]

    @Capt J:
    you are correct ref. the fuel circulating being well above the max fuel burn, but according to the MAN manual the pump moves 198 GPH at the max rpm (2300), so the 285 GPH the filter can handle still gives a decent margin.
    The 5-10 PSI vacuum at cruise speed that you mention, is it referred to the same brand and size of filters?And with which engines?
    Ideally, it would be great to hear from anyone who experienced the same filters/gauges with MAN engines...
  6. Capt J

    Capt J Senior Member

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    It doesn't matter WHAT primary fuel filters you have, with clean and appropriately sized filters/fuel lines/fuel vents generally every single yacht I've run with Racors or Separs or Dahls would be around 5-10 psi of vaccuum at cruise rpm with clean filters, most generally around 5psi.....but this depends on the length of the fuel line run...........So run yours at cruise for 20 minutes or so, go in the engine room while still at cruise and see what vaccuum you have as your baseline, then have someone go to WOT and see if it stays the same just for comparison. If you see over 10 psi more at cruise than your baseline, I'd start changing filters....... 15 psi more.....definately and I would'nt run filters are 20 psi period.
  7. d_meister

    d_meister Senior Member

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    the following pic shows you the scale better, but why do you think the position at rest should be relevant?
    I mean, I understand that the static position can be affected by the tank position, and also by how full they are, but for the intended purpose of the gauge, its reading is only relevant while fuel is circulating, "sucked" by the engine fuel pump and possibly restricted by a clogged filter.
    So, the position at rest should be irrelevant - or am I missing something?
    [​IMG]
    It's by way of explaining what may occur. If there's positive head from a tank with fuel level higher than the gauge, there may be pressure on the gauge. I mention it in the event you become concerned that the gauge doesn't "zero" at rest. In terms of operation; it's just an anomaly Actually that little vent is there to permit pressure equalization It was the situation, once upon a time, that there was no toggle in these gauges, and pressure would accumulate inside the gauges causing them to appear stuck. The cure was to remove the rubber plug to equalize. There are many gauges out there now that have lost the plug into the interior of the gauge, or lost elsewhere in the engine spaces.
  8. mapism

    mapism Senior Member

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    Very interesting to hear that, also because you seem to confirm that these gauges are frequently installed in boats at your side of the Atlantic, right?
    Don't ask me why, but in Europe they are as rare as hens' teeth.
    I can only remember to have ever seen them on a very old Akhir - and only statically.

    Besides, I wouldn't have expected the baseline to be so similar between different boats, with different fuel lines/tanks/primary filters.
    That's also a useful reference: if by chance in my installation they should show say 20 psi right away, with fresh cartridges, maybe there would be something else to be concerned about.

    I will post my findings in due course, but thanks a lot for the moment.
  9. mapism

    mapism Senior Member

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    All understood, thanks.
    In fact, I was also wondering how/why the air bubble could disappear.
    I mean, other than thermal dilatation of the fluid inside, that could temporarily reduce the air bubble, what else could fill the air space and leave the gauge interior permanently filled?!?
  10. Capt J

    Capt J Senior Member

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    Yes, the gauges are common over here. You don't see them due to your yachting regulations, the same as how you guys have metal bowls on all of your fuel filters and we have clear sight glasses on the bottom of all of our primary fuel filter housings. They're very common here, not every yacht has them, but a very good amount of them do. If you see 20 PSI with fresh filters then you have a restriction such as a clogged fuel vent, fuel hoses not large enough or a collapsing hose. You will see a slightly higher vaccuum if say you switch fuel valves from an engine room tank to a bow tank that's 40' away generally, but maybe only 1-2 psi.

    The bubble in the gauge will never disappear, it is mineral oil and separ didn't fill the gauge with enough mineral oil to fill the entire housing. It won't hurt anything, but it would annoy me enough that I'd return it and get another one and check it in the store but tipping it straight up. The mineral oil just acts to steady the gauge needles and help protect them from damage from vibration.

    The gauge reading is only relevant really at cruise speed or more when you're demanding more fuel from your filters.......at idle speed in neutral even the most clogged of fuel filters will still flow enough fuel for the engine to run. You want to turn the red needle to zero, then see where it ends up after running at cruise.
  11. mapism

    mapism Senior Member

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    I am not sure of what the EU regulation restrictions are on fuel filters (if any), but while metal bowls are indeed common, actually also sight glass bowls are not rare at all, also in OEM installations.
    My boat is just one example, but I can think of several others.
    They did fit the version with metal heat deflector though, which as I understand is also USCG accepted, but frankly I don't know if that was a requirement from RINA (the certification authority) or not.
    Anyway yes, indeed I've only seen vacuum gauges on one old boat (and they were probably retrofitted), while I've seen them in several boats in the US.

    Ref. the 20 PSI with fresh filters, that's not what I'm expecting, because the engines never had any fuel problem so far, and I fitted the gauges just for the convenience of having an early warning.
    It was a number I used as a hypothetical example of something obviously strange.
    20 PSI would be even off-scale on the gauge...

    Lastly, the reference red needle just happened to be there when I took the pic, I will reset it to zero before running the engines.
    But are you sure it's supposed to be "pushed" by the working black needle, in order to stay at the maximum vacuum reached after running?
    It seems rather stiff, when rotating it with the knob, so I doubt that the working black needle can move it.
    And both the new gauges that I bought behave exactly in the same way (and have the same air bubble), so it seems unlikely that both are defective in the same way...
  12. Slimshady

    Slimshady Senior Member

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    Question for the group, which filter, separ or racors has the most surface area. That would indicate the potential filter capacity before clogging. I do not remember seeing it on either of the two filter manufacturers data sheets.
  13. Capt J

    Capt J Senior Member

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    Racor has much more surface area, is much easier to change, and elements are much cheaper and you can find them anywhere. The only advantage separ has is it's a smaller height.

    Sorry Mapism, I meant 20 Inches of vaccuum. The only way you'd see any real pressure (PSI) would be if it was connected to an electric fuel pump and you were using the Filter on the supply side as a polishing system. Yeah the RINA standard that requires a heat proof bowl (the metal cup on racor's and separs). We don't have that here. BUT, I don't think the gauge is RINA approved, is my guess why you don't see them. On the dual racor 1000s or dual 500's, they come with the gauge built in automatically so you see them on the yachts.
    Last edited: Jun 21, 2020
  14. Slimshady

    Slimshady Senior Member

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  15. Slimshady

    Slimshady Senior Member

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    Thank you for the response
  16. Capt Ralph

    Capt Ralph Senior Member

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    The rubber cap or plug has been replaced with a small valve. That lil yellow tail is the valve. As pictured it is closed.
    This is also NOT a temperature compensated gauge. More on that later.
    Install the gauge in it's final position, Hopefully very up-rite.
    Let it sit over night.
    Push that lil flag to the open position to release the air. Some (maybe a small drop) glycerin oil may come out also. This is O K.
    The black needle should now center over O. Do not touch the gauge case or face yet, with your finger tip, close the lil yellow valve.
    You may have noticed just by pushing the gauge face lightly, the needle will move. This is why nothing should ever be laying on the gauge case like a hose or wire run.

    Remember; This is not a temperature compensated gauge. This is why the gauge had to sit over night to warm up and settle to the new environment. If this meter is close to the engine, as it warms up, it may become off zero. You will need to learn it's movement and figure vacuum from it's new starting point. Do not try to zero the gauge when it's hot, more glycerin oil will come out of the valve. Then, when it cools, it will draw air in, make a bigger bubble that will never go away.

    The other needle is the tell tail. Zero it also with the lil knob on the dial face. It will show you the max swing the black needle moved so you don't have to crawl into the ER while operating.
  17. d_meister

    d_meister Senior Member

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    The color coded legend on a Racor vacuum gauge pretty much tells you what you should expect in terms of normal operation:
    [​IMG]
    Here are more images of fuel suction gauges, all with similar ranges.
  18. mapism

    mapism Senior Member

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    Thanks for the detailed explanation on the yellow little valve.
    I finished installing the new covers & gauges yesterday (yes, perfectly up-rite).
    So, even if I had not read your post yet, by coincidence they did sit overnight unmolested.
    Now, I just tried putting the yellow valve on "open", and nothing happened, and not even the smallest drop of glicerin came out, so after a while I put it back on "close"

    Statically, the black needle actually isn't exactly on zero, but just very slightly on the pressure side - barely noticeable, actually: less than one psi.
    I guess this is because the tanks are almost full, and their max level is somewhat higher than the gauges.
    Both gauges are consistent anyway, so I don't think they are defective.
    I also tried pushing the glass faces a bit, but they feel very solid, and I could only see the air bubble veeery slightly reacting to pressure.
    The needles didn't move.

    Another thing I checked is how the tell tale red needle works, and I can confirm that both you and Capt J were correct:
    if I rotate it clockwise, it drags the black needle together with it.
    And when rotated CCW, the black needles follows, up to its zero position (well, just above as I explained, but let's call it zero).
    So, obviously when the opposite will happen (i.e. it's the black needle rotates CCW due to vacuum), the red tell tale must be dragged up to the max swing reached by the black needle while the engines are running, which is indeed very convenient.

    I can't yet make a full live test now with the engines running, but as soon as I will be able to make it, I'll report back.
    In the meantime, thanks a lot everybody.
    Amazing how after decades fiddling with boats there is always some bit of kit on which to learn something new! :)
    Last edited: Jun 22, 2020