Vacuum gauge

[Capt.Don]

Yanmar 3GM30F - I'm installing Racor vacuum gauge RK-11233 with an inline tee on the fuel outlet hose of my Racor primary filter (245). I've verified that the gauge works by sucking on the hose. However, when running the diesel, the gauge barely moves, and doesn't read any vacuum pressure.

This may be good, but I'm surprised by this, as I'd expect some soft of reading. The gauge is about the same level as the Racor fuel filter, and about 6" above the engine and a couple inches above the bottom of the fuel tank.

The instructions say there's a pin to reset or zero the gauge. Do I need to do this and would that unlock the gauge? Does fuel need to be in the tee segment going to the gauge? If so, how do you fill the hose with fuel and attach to the gauge? I've tried everything and only managed to spill diesel everywhere. I don't want a pocket of air in the system.

I appreciate any advice. Thank you
Don

[DeepFrz]

With that small engine and a clean filter you wont see much of anything. As the filter gets dirty the vacuum will rise. I hope it is the gauge with the tell tale needle.

[Roy M]

Give it a little time. Have you given any thought to installing a second, backup filter and switch? If you notice the filter is drawing hard, just as you are entering a spooky channel, you can switch to a clean filter almost instantly.

[Capt.Don]

I've got about 250 hours on the current filter. No signs of dirt, water, etc., in the filter. I would have thought the vacuum would register some pressure. I'll leave it installed and watch.

Any thoughts on the air in the line from the tee to the gauge? Will it work itself out or is this an airblock waiting to move to the main fuel line?

A dual filter is on my wish list! I thought I'd install the vacuum gauge first.
Thanks
Don

[rigormortis]

I have also installed recently a Racor-Parker vacuum gauge using the T-system downstream of the Racor filter. When I suck on the hose the needle moves but it shows no signs of movement from 0 when engine is running. I have a Yanmar 4jhE? non-turbo 4 banger. I suppose I could gradually clamp the fuel line upstream of the vacuum gauge (after Racor 500 filter) but don't want to compromise the fuel lines.
Hell, the engine runs. I watch the gauge from time to time and have no room to install a 2nd Racor so I guess I live with it and hope for the best. Sounds like normal sailing philosophy.
Pete

[Maine Sail]

In order to read a vacuum gauge the engine should ideally be at loaded cruise RPM.. Even with a filter that may cause restrictions at cruise RPM you may read zero at idle..

This is why a drag needle or drag pointer gauge is nice.. The highest vacuum is recorded so you can check it any time...

[Roy M]

The bubble is normal (see the pic above). It's not air in the line. It drives everyone, who doesn't know about it, nuts thinking something is wrong. I located my gauge in the cockpit, right on the instrument panel. It also has a vacuum switch, attached to the back of the gauge, that activates a buzzer and idiot light above the gauge to let me know something is getting blocked up

[Capt.Don]

It sounds like I won't see much of a vacuum reading until the filter starts to block the flow and the engine is under load. I'll keep an eye on this (after all that's why I installed the gauge). The Racor gauge came with a red sticker, not adjustable needle.

The air pocket I'm talking about is in the 6" branch of fuel hose, tee'd off of the main fuel line. I basically tapped off the output of the primary filter with a 1/4" brass tee, with the branch lead to the gauge. I may be over analyzing this, as the pressure builds on the line, some of the air in the short branch will be drawn through the tee and into the main fuel line. I can imagine this bit of air being pumped through the fuel system and causing the Yanmar to stall. Perhaps as the boat moves around and pressure fluxuates , small pockets of air are released, ultimately forcing fuel back into the tee'd branch. I would love to understand the fluid dynamics of this system

I will wrap-up this project and hopefully stop worrying about air pockets stalling my diesel. At least, one of the benefits of this project is having to bleed the diesel a few times.

Thanks for all the comments and pictures of your setups.

Don

[Roy M]

I have installed an outboard motor fuel bulb in my diesel fuel line between the tank and the filters to help speed up the purging of air. You can actively get rid of any air in the line with one of these, cheaply. I once had a customer that complained that the fuel bulb had collapsed and shut off the flow of fuel. I explained that the collapse was a symptom, not the cause of his problem. We turned the bulb 180 degrees, pumped it a couple times, then reversed it back to its normal position. It turned out that he had a plug of fiberglass strands that had blocked the tank pickup tube, and we were able to blow it out, and later clean the tank of any debris. Actually, I have two such pumps. One before the filters to help fill them when changing. The other is just before the "tickler" pump lever on the fuel pump, which I find almost useless when trying to bleed the engine, hence the higher capacity (and pressure generated) outboard bulb. Speed can be of the essence when needing to bleed a diesel.

[a64pilot]

small amount of air in you diesel fuel I believe will sort of be self bled out and will be returned to the tank via the return fuel line. The vapor pressure of Diesel is pretty high so I think it would be real hard to vapor lock one I think, vapor lock is sort of like prop cavitation, the pressure is reduced to where the liquid at the lower pressure is above it's boiling point and what looks like air is actually liquid vapor. Either way a Diesel seems to be able to tolerate a small bubble of air from time to time

[Capt.Don]

I'm going to declare this project complete. I will watch the gauge under power and hope that the bit of air in the branch from the tee doesn't block the main fuel line. Thanks for all your input, ideas and photos!