Non return valves.

[pandos]

I want to renew the fuel system on my md21b.

I have a new lift pump en route and I am going to replace the cav filter holders with spin on Bosch type so there are less opportunities for air ingress.

I would also like to create a separate backup system with a 12v pump and separate filter directly into the injection pump.

To do so I obviously need to stop the fuel from one system passing out through the other.

In stead of taps/ manual valves I wonder could I simply insert non return valves..?

In theory if I have a problem with the main side I could just power up the secondary system and at worst bleed the injection pump and away I go... No need for fault tracing / repairs etc...

I hope a gauge (vacuum) in the main system might indicate a problem before engine stopped...

I think too high a vacuum could indicate a blocked filter and too low a vacuum could indicate ingress of air?

 

[pvb]

I reckon that manual valves will be more reliable than non-return valves.

After an experience with diesel bug, I fitted a vacuum gauge on my last boat. It was very useful as an indication of when the primary filter started to get clogged.

 

[pandos]

I reckon that manual valves will be more reliable than non-return valves.

After an experience with diesel bug, I fitted a vacuum gauge on my last boat. It was very useful as an indication of when the primary filter started to get clogged.

Where in the system did you fit the gauge.. any chance of a link to the source.

I am trying to avoid fitting anything bulky or cumbersome onto the engine and I'd rather not take everything off for remote mounting.. i agree manual valves might be more reliable but they would require complicated pipework which might be counterproductive. In terms of introducing weak points....but I'll certainly have a look when I get the bits back together and dry fitted...

 

[rogerthebodger]

If the electric pump you are planning to fit and the ones with a oscillating piston there have 2 non return valves built in.

I fitter one of there as a priming pump just before my primary and in series with the main engine mechanical lift pump.

Works OK until the non return valve got grit jammed in the valve so it would not close. I then fitted a sediment filter between the tank and the primer pump

 

[pvb]

I just put a T-joint in the fuel line from the primary filter to the lift pump, and piped the vacuum gauge to the T-joint. The gauge I fitted was a Racor gauge, which was oil-filled and damped. Cheaper vacuum gauges are available on eBay, etc. When the vacuum reading reaches about -30kPa, it's time to change the filter element.

 

[pandos]

How does a vacuum gauge operate if it is not almost at the fuel line.

If it is in a cul de sac will this line need to be bled or can the air in it end up in the fuel system am I over thinking this.?

I use a 12v priming pump before the lift pump so am I in danger of damaging a gauge ... ?

 

[pvb]

How does a vacuum gauge operate if it is not almost at the fuel line.

If it is in a cul de sac will this line need to be bled or can the air in it end up in the fuel system am I over thinking this.?

I use a 12v priming pump before the lift pump so am I in danger of damaging a gauge ... ?

The pressure (or vacuum) in a pipe system is equalised throughout, so the gauge will see the same vacuum which the filter experiences.

It doesn't need to be bled. The gauge is sealed, so air won't enter the fuel system through it.

A priming pump won't damage the gauge.