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Old 26-01-2016, 09:11   #1
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Vacuum Gauge Recommendations?

Hello Everyone,

We have a 1980 Perkins 4-108 in our Cal 39 which has dual Racor primary fuel filters so that you can switch from one to the other if the element in one gets plugged and it isn't convenient to change it out on the spot.

We have been told we really ought to have a vacuum gauge hooked into the fuel system so we can monitor the state of the elements in the filters. As they progressively plug up, the vacuum will go up and the gauge will tell us when we have to change the elements without having to pull apart the filters to check visually.

My guess is that it would be hooked into the line from the primaries to the secondary filter so it would work with whichever primary filter we happened to be using; but I'm not really sure.

I have been looking for a gauge and have found many online priced from about $40 to well over $100. Being retired and on a tight budget, we're hoping to find one as inexpensive as possible. One supplier told me their gauges won't work with liquids. There's more to this vacuum gauge business than I anticipated.

Can anyone out there recommend a vacuum gauge that will work?

Where could we get one?

Once again, we appreciate your help.
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Old 26-01-2016, 11:25   #2
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Re: Vacuum Gauge Recommendations?

We have a Racor gauge we installed about 25 years ago and still working well. It is not the type that screws into the top of the Racor but in the downstream line. I would check defender or West marine as a quick starting point

Good luck

Chuck



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Old 26-01-2016, 11:50   #3
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Re: Vacuum Gauge Recommendations?

If you're trying to do things on the cheap, the best way is to make your own liquid manometer. All you need is a simple u-shaped length of clear tubing filled with water, with one end vented to atmosphere and the other attached to the chamber you want to measure the pressure of. The difference between the two sets the pressure.



Atmospheric pressure is 10^5 Pa, i.e. equivalent to 10 tonnes per square meter of water. That is equivalent to a 10m tall column of water above it, so every cm of difference in water pressure is equivalent to 100 Pa or 1 mBar. If you need to measure much larger pressures it is possible to use Mercury instead of water, but I would strongly recommend not doing so.

The big advantage of a system like that is that it's dirt cheap and essentially foolproof - the only thing to do wrong is if the pressure differential gets so great the water is sucked in or it just evaporates. In the first case it's long past time to change your filter anyway, and in the second just top the water up.

Failing that get hold of the cheapest capsule dial gauge you can find, but personally I'd just stick with a manometer.
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Old 26-01-2016, 11:53   #4
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Re: Vacuum Gauge Recommendations?

Racor sells a gauge, specifically for that purpose, I believe
I know my dual filter set-up has one, and has a "tattle tale" that tells you max vacuum.

Here is a couple, I link to defender only as they have good pictures

http://search.defender.com/?expressi...+Gauge&x=8&y=9
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Old 26-01-2016, 12:56   #5
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Re: Vacuum Gauge Recommendations?

I looked for but couldn't find a drag needle vacuum gauge in the UK.
Think designatedengineer.com in the US sells them though.

Bought two non-drag needle gauges for about 21 the pair on ebay, plan is to remote connect so I can see them from the steering position.

Instrument specialist company's response to my question about drag needle vacuum gauge:

"Sorry but vacuum gauges do not work well with a drag pointer.
The movement is very light on these and the effect of the drag will make them much less accurate.
These are OK on fairly high pressure gauges with more force but not low pressure or vacuum, so unable to help with this."

Wasn't fully convinced but it did make me wonder if a drag needle could conceivably stick or become loose over time.
Must be possible mustn't it?
Decided that either failure could give a false sense of security.
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Old 27-01-2016, 08:43   #6
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Re: Vacuum Gauge Recommendations?

Quote:
Originally Posted by chouliha View Post
We have a Racor gauge we installed about 25 years ago and still working well. It is not the type that screws into the top of the Racor but in the downstream line. I would check defender or West marine as a quick starting point

Good luck

Chuck



jacaranda-journey
That's just what I'm looking for. thanks!
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Old 27-01-2016, 08:45   #7
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Re: Vacuum Gauge Recommendations?

Quote:
Originally Posted by pdf27 View Post
If you're trying to do things on the cheap, the best way is to make your own liquid manometer. All you need is a simple u-shaped length of clear tubing filled with water, with one end vented to atmosphere and the other attached to the chamber you want to measure the pressure of. The difference between the two sets the pressure.



Atmospheric pressure is 10^5 Pa, i.e. equivalent to 10 tonnes per square meter of water. That is equivalent to a 10m tall column of water above it, so every cm of difference in water pressure is equivalent to 100 Pa or 1 mBar. If you need to measure much larger pressures it is possible to use Mercury instead of water, but I would strongly recommend not doing so.

The big advantage of a system like that is that it's dirt cheap and essentially foolproof - the only thing to do wrong is if the pressure differential gets so great the water is sucked in or it just evaporates. In the first case it's long past time to change your filter anyway, and in the second just top the water up.

Failing that get hold of the cheapest capsule dial gauge you can find, but personally I'd just stick with a manometer.
Thanks! This is an ingenious idea. Definitely food for thought.
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Old 27-01-2016, 08:51   #8
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Re: Vacuum Gauge Recommendations?

Quote:
Originally Posted by a64pilot View Post
Racor sells a gauge, specifically for that purpose, I believe
I know my dual filter set-up has one, and has a "tattle tale" that tells you max vacuum.

Here is a couple, I link to defender only as they have good pictures

Defender.com Search Results: Racor T Handle Vacuum Restriction Indicator Gauge
This is a huge help. Points me in the right direction. Thanks!
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Old 27-01-2016, 22:51   #9
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Re: Vacuum Gauge Recommendations?

On Amazon, $10-15. $15 is oil filled and free shipping w/prime.Most gauges will work. If your fuel pump is a diaphragm and has heavy pulses, you may need a oil filled gauge. You know because the needle sweeps back and forth. The oil dampens the pulses. Also good where a gauge is near a pump outlet.
The gauge goes between the filter and engine. Mine is an old gauge I pulled out of a drawer and it could be 30 years old. Accuracy isn't important. The difference between new and dirty filters is what you need to know. On my system, Racors w/2 micron filters going into a fuel manifold, the gauge reads 0 with a new filter and I change at 10".
Most boats have a 30 micron in their primary. I can have a 2 micron because my tanks are clean and I'm careful about where I buy fuel.
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Old 27-01-2016, 23:56   #10
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Re: Vacuum Gauge Recommendations?

I know this isn't what you asked, but...

instead of a vacuum gauge, I prefer to add a lift pump near the fuel tank. This gives several advantages.

1. You never lose prime.
2. Filters under vacuum will only wet enough surface area to overcome the vacuum, which in the beginning isn't much area. As the lower filter media clogs, vacuum pulls the fuel up to a higher level in the filter to pass through unclogged filter media until finally the filter clogs completely. A lift pump pressurizes the entire fuel system and fills the entire filter, wetting all of the media and passing fuel through all of the pleats simultaneously until the filter clogs completely. I'm not saying that the filter lasts longer, but it will filter better right up until it does clog.
3. If you do develop a leak in your fuel system, it will drip, making it easy to find, as opposed to leaking air into the system, which is the #1 cause of diesel engines dying or not starting - loss of prime. These air leaks are very hard to find.
4. After replacing a filter, just crack the bleeder screw and let the pump fill the filter up and drive all of the air out.
5. When diesel fuel is under vacuum, entrained air can get released from the fuel and cause problems for the injection pump, which is expecting a noncompressible fluid but instead gets a foamy mixture which compresses and lowers injector pressure, especially on common rail fuel systems. This problem really came to light when common rail injection was used on light and medium duty trucks, some of them gave slightly lower power output and markedly lower fuel economy numbers.
6. They're not that expensive, probably the same price as a new vacuum gauge.
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Old 28-01-2016, 00:03   #11
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Re: Vacuum Gauge Recommendations?

Also, a word about fuel filters which I haven't seen brought up since I've been a member. I know Racor is a good brand name in filtration, but the ratings of the filters should be looked into. There are filters that are nominally rated and others are absolute rated.

Instead of trying to explain it myself, here's a quote from a website about it.

Quote:
Absolute rating vs. nominal rating for filters
Filters are rated on their ability to remove particles of a specific size from a fluid, but the problem is that a variety of very different methods are applied to specify performance in this way.
Pore size ratings refer to the size of a specific particle or organism retained by the filter media to a specific degree of efficiency. A filter that is marked '10 micron' has some capability to capture particle as small as 10 micrometers. However you do not know exactly what this means unless you also have a description of the test methods and standards used to determine the filter rating.
The two most used reported media ratings are nominal and absolute micron rating.

Absolute rating

The absolute rating, of cut-off point, of a filter refers to the diameter of the largest spherical glass particle, normally expressed in micrometers (mm), which will pass through the filter under laboratory conditions.
It represents the pore opening size of the filter medium. Filter media with an exact and consistent pore size or opening thus, theoretically at least, have an exact absolute rating.

The absolute rating shouldn't be confused with the largest particle passed by a filter under operating conditions: the absolute rating simply determines the size of the largest glass bead which will pass through the filter under very low pressure differentials and nonpulsating conditions.

This does not usually apply in practice: pore size is modified by the form of the filter element and it is not necessarily consistent with the actual open areas. Furthermore the actual form of the contaminants are not spherical and the two linear dimension of the particle can be very much smaller than its nominal one, permitting it to pass through a very much smaller hole (i.e. cylindrical particles with a thickness less than the slot opening of the filter).
The passage of oversize particles in this manner depends very largely on the size and shape of the opening and on the depth over which filtering is provided.
Most of filters generate a filter bed: contaminants collecting on the surface impart a blocking action decreasing the permeability of the element bad improving filter efficiency. When the blocking is so severe that the pressure drop is excessive, the flow rate through the system decrease seriously. This explains why the performance of a filter can often exceed its given rating based on the performance of a clean element and why test figures can differ widely with different test conditions on identical elements.

It may be argued that the term absolute rating is not a realistic description. Strictly speaking the term absolute indicates that no particle larger than that rating can pass through the filter, limiting the type of media to those of consistent pore size where they show 100% retention of particles.

Nominal rating

The nominal rating refers to a filter capable of cutting off a nominated minimum percentage by weight of solid particles of a specific contaminant (usually again glass beads) greater than a stated micron size, normally expressed in micrometers (mm). I.e. 90% of 10 micron.
It also represents a nominal efficiency figure, or more correctly, a degree of filtration.
Process conditions such as operating pressure, concentration of contaminant etc, have a significant effect on the retention of the filters. Many filter manufacturers use similar tests but, due to the lack of uniformity and reproducibility of the basic method, the use of nominal ratings has fallen into disfavor.

Mean filter rating

The mean filter rating refers to the measurement of the average pore size of a filter element. It establishes the particle size above which the filter starts to be effective. It is determined by the bubble point test and it is more meaningful than a nominal rating and, in casa of filter elements with varying pore size, more realistic than an absolute rating.



Read more: Absolute rated filters vs nominal filters - Lenntech
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Old 28-01-2016, 00:52   #12
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Re: Vacuum Gauge Recommendations?

Quote:
Originally Posted by socaldmax View Post
I know this isn't what you asked, but...

instead of a vacuum gauge, I prefer to add a lift pump near the fuel tank. This gives several advantages.

1. You never lose prime.
2. Filters under vacuum will only wet enough surface area to overcome the vacuum, which in the beginning isn't much area. As the lower filter media clogs, vacuum pulls the fuel up to a higher level in the filter to pass through unclogged filter media until finally the filter clogs completely. A lift pump pressurizes the entire fuel system and fills the entire filter, wetting all of the media and passing fuel through all of the pleats simultaneously until the filter clogs completely. I'm not saying that the filter lasts longer, but it will filter better right up until it does clog.
3. If you do develop a leak in your fuel system, it will drip, making it easy to find, as opposed to leaking air into the system, which is the #1 cause of diesel engines dying or not starting - loss of prime. These air leaks are very hard to find.
4. After replacing a filter, just crack the bleeder screw and let the pump fill the filter up and drive all of the air out.
5. When diesel fuel is under vacuum, entrained air can get released from the fuel and cause problems for the injection pump, which is expecting a noncompressible fluid but instead gets a foamy mixture which compresses and lowers injector pressure, especially on common rail fuel systems. This problem really came to light when common rail injection was used on light and medium duty trucks, some of them gave slightly lower power output and markedly lower fuel economy numbers.
6. They're not that expensive, probably the same price as a new vacuum gauge.

Hi, glad to know I'm not the only one who thinks this way.

I know Racor says pump should be on the negative pressure side, but I think they accept that a <15psi pump is OK pushing - very much my own preference.

Wondering if their reason is that a positive pressure pump could collapse the element?

Facet red top (type) 4-6 psi on ebay is just over 20, cheap enough to carry a spare.

Been holding off buying through lack of confidence in my own judgement - now I have someone to blame when the lifeboat turns up... Thanks!
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