Diesel filter vacuum gauge, and CAV.

[prv]

I've always been aware of the potential for filter clogging, but having had the engine in the new boat die because of it on our very first trip (just motoring up Southampton Water for delivery purposes) I'm more keen than ever to avoid a repeat.

As part of the new fuel system I want to have a vacuum gauge for early warning of a filter beginning to block. I know ASAP sell some with the Racor name on them, but they seem very expensive for what they are. Do the experts think this: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=130849158329 would do the same job?

Also, what about the actual filters to use? On KS I took in several dire warnings here about how rubbish CAV filters are, and went for Racor spin-on units. Actually, CAV would have been a problem there due to limited access, but on the new boat I'll be placing them somewhere very convenient and having a changeover valve to boot, so the "they have lots of fiddly pieces" argument doesn't really apply. Given that Volvo still seem to specify this type, and I have two handy already (one currently fitted, one in the shed originally from KS) is there any good reason to prefer something else?

Cheers,

Pete

 

[Rossynant]

Look for truck or tractor parts, something suitable might be cheaper; no reason for "marine supply" really, CAV type filters are not "marine" anyway.
More important is to have a prefilter with water/dirt separator, see-through glass and drain; this was standard for boats, time past.
Can't comment on gauge quality, but then why not? Just a gauge.

P.S. still have a glass separator aboard, 40 years old that now would not be "permitted" as it's glass, can break so a glass one I had in a 4x4 car, obsolete, couldn't even get element for it but worked long years.
For cheap - CAV filter: http://www.thornycroftparts.co.uk/T...lass_Diesel,_Bio_WVO_UNF/p207754_4307209.aspx

 

[pvb]

I've always been aware of the potential for filter clogging, but having had the engine in the new boat die because of it on our very first trip (just motoring up Southampton Water for delivery purposes) I'm more keen than ever to avoid a repeat.

As part of the new fuel system I want to have a vacuum gauge for early warning of a filter beginning to block. I know ASAP sell some with the Racor name on them, but they seem very expensive for what they are. Do the experts think this: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=130849158329 would do the same job?

Also, what about the actual filters to use? On KS I took in several dire warnings here about how rubbish CAV filters are, and went for Racor spin-on units. Actually, CAV would have been a problem there due to limited access, but on the new boat I'll be placing them somewhere very convenient and having a changeover valve to boot, so the "they have lots of fiddly pieces" argument doesn't really apply. Given that Volvo still seem to specify this type, and I have two handy already (one currently fitted, one in the shed originally from KS) is there any good reason to prefer something else?

The vacuum gauge is a good idea. I fitted a Racor one years ago, and it's been useful. You can see the vacuum start to increase as the filter progressively gets dirty. It also means that you needn't change filters until you they actually need changing! The eBay gauge should be fine; it has the same calibration range as the Racor one.

In terms of plumbing, you should ideally have 2 separate filters with isolating valves on the input of each, and on the output of each. You'll then be able to isolate one filter totally, to change it whilst the engine's running. However, unless your tank is higher than the filters, you'll need to include a rubber priming bulb if you want to bleed a new filter whilst the engine's running.

Note that the double filter suggested by Rossynant is permanently plumbed internally for the 2 elements to be used in parallel - you cant isolate one.
CAV filters are fine if you have room to access them. Spin-on filters are better if you're mechanically challenged, but are more expensive.

 

[pvb]

For cheap - CAV filter: http://www.thornycroftparts.co.uk/T...lass_Diesel,_Bio_WVO_UNF/p207754_4307209.aspx

Err... that's far from cheap! SSL Diesel Parts are much cheaper for most filters...
http://www.ssldieselparts.co.uk/filter-assemblies-c-267.html

 

[ghostlymoron]

That's a quite small pressure range. It might always indicate maximum vacuum but i suppose for a fiver its worth a try.

 

[pcatterall]

I used an ebay one for sub £5 it works fine, I will have to fit some kind of damper though as the guage is close to the pump and 'flickers' in response, still easy to read.

 

[vyv_cox]

My experience with CAV ones is far from great. Fitting the seal to a tapered seat against the glass bowl can be very tricky and I have struggled several times to get mine leak free.

 

[pvb]

That's a quite small pressure range. It might always indicate maximum vacuum but i suppose for a fiver its worth a try.

I assume you don't have a vacuum gauge. I have, and that eBay gauge will be fine. It's the same range as the Racor gauge. Once vacuum gets to about 12"Hg (less than half max scale), the filter is pretty dirty and needs changing.

 

[Talulah]

Irrespective of which gauge you fit (we fitted a Racor one from ASAP Supplies) it will over time pay for itself. No longer do we routinely replace filters.

 

[ghostlymoron]

I assume you don't have a vacuum gauge. I have, and that eBay gauge will be fine. It's the same range as the Racor gauge. Once vacuum gets to about 12"Hg (less than half max scale), the filter is pretty dirty and needs changing.

Sorry yes you're right. i was looking at the pic on my phone and thought it was only down to 0.1 bar.

 

[prv]

In terms of plumbing, you should ideally have 2 separate filters with isolating valves on the input of each, and on the output of each. You'll then be able to isolate one filter totally, to change it whilst the engine's running. However, unless your tank is higher than the filters, you'll need to include a rubber priming bulb if you want to bleed a new filter whilst the engine's running.

Thanks, yes, I'm well aware of all this having built just such a system for the old boat. The one for the new boat will be even better, incorporating my experience with the old one.

I really wanted to know whether that gauge was ok (the Racor one appears to be fluid-filled, and this one isn't) and whether other filter systems are sufficiently better than CAV for me to use them instead of the two CAV housings I already have.

Pete

 

[pvb]

I really wanted to know whether that gauge was ok (the Racor one appears to be fluid-filled, and this one isn't) and whether other filter systems are sufficiently better than CAV for me to use them instead of the two CAV housings I already have.

Yes, the Racor one is fluid-filled, I'm not sure whether that improves it or not. The Racor one has a little rubber bung in the back, too, which enables the gauge to be reset to zero (it drifts as atmospheric pressure changes). In practice, I just leave mine alone and mentally note the starting point when the engine's off. Mine is connected to the fuel lines straight after the primary filters, and doesn't show any fluttering of reading. The eBay one is so cheap that if it's not satisfactory you could change it for a better one.

I have a couple of CAV primary filters. I find the easiest way to change elements is to put a plastic container underneath and just lower the glass bowl and filter element into it. As long as you realise that there are 2 different diameters of the large sealing rings, I can't see that CAV filters are particularly difficult to work on.

 

[prv]

Yes, the Racor one is fluid-filled, I'm not sure whether that improves it or not.

I've had a reply from the ebay seller, who seemed knowledgeable. He says the glycerine fill is for damping, so that rapidly fluctuating pressure doesn't shake the mechanism back and forth and damage it. You say yours doesn't show any fluttering, so the fluid seems unnecessary here. I'm going to order that gauge tonight.

I can't see that CAV filters are particularly difficult to work on.

I agree - I was more curious about their performance as filters. Some here have opined that they are crude and primitive compared to alternatives.

Pete

 

[pvb]

I agree - I was more curious about their performance as filters. Some here have opined that they are crude and primitive compared to alternatives.

The filter elements aren't wonderful, but most engines have a fine secondary filter fitted, so the chances of rubbish getting through to the injection system are slim. CAV elements do a cheap and cheerful job of filtering out the worst of the crud.

 

[WoodyP]

To me the great advantage of CAV filters is that they are cheap. If you have a bit of a fuel problem then you can carry half a dozen to change without needing a mortgage. I have never, ever had a problem putting them back to gether and don't understand why the cack handed spanner monkey's don't like them

 

[vyv_cox]

and don't understand why the cack handed spanner monkey's don't like them

I bow to your superior abilities. Having spent a considerable period of my younger years repairing motor vehicles to supplement my income, in addition to being employed in a very practical position in a high tech industry, I would not classify myself as a 'cack-handed spanner monkey'. Nevertheless I think the design of the CAV filter, where a sealing O-ring is required to function on a tapered seat, is a poor design that is far from easy to assemble correctly in non-ideal circumstances such as hanging down over a bilge.