Fuel dampener

[MinamiKotaro]

I'm redoing my fuel lines and would like to add a fuel dampener to the fuel rails. I may put one on each, depending on how I end up routing the lines. Does anyone know of a damper that will fit 1/4 NPT (CB fuel rails)? Most seem to be 3/8 NPT. I'd like to avoid using an adapter.

[andy198712]

Interesting, I'd never heard of these before! There used in Hydrualic systems a lot to allow for pump pulses and loss in pressure but also ram displacement.... Boring lesson over!

[MarioVelotta]

I haven't seen any 1/8" npt, but I think Volvo has a 1/4" npt or banjo version. I would also like to fit one into my new fuel rails when I complete the one with an integrated regulator.

[MinamiKotaro]

Well, I made one out of a tee, a pipe nipple, and a cap. We'll see if it makes any noticeable difference.

[Piledriver]

I doubt it will help much w/o the diaphragm and spring.

There's a herd of them on ebay for various cars, worst case install a pipe nipple.
The Kia ones look like a possibility, just note some Kias (all?) are GDI now.

Note that a lot of the Ebay Bosch "dampers" are regulators if you look at the pics and part#s.
Idiots.

The old CIS ones ran at ~50-60 PSI, usually, the CIS-M closer to 85.
Large volume though, easily 20X the little ones meant to go on the rail.
Cheap too.

Mounted somewhere on the crossover line (about 1/2 way) world probably do the most good.

[thedrew]

whats the point of it? I have a fuel pressure sensor and I see my fuel pressure oscillate maybe +/-1psi while driving.

[Piledriver]

Are you running 1000cc injectors and a huge turbo?

Even not using huge injectors, many OEMS still see a need for them.

[Steve Arndt]

CIS Benz cars have one that is built into a pretty little alloy swirl pot. I've saved a couple out of the recycle bin at our shop. I'll post up a pic. I've considered trying one.

[MinamiKotaro]

I doubt it will help much w/o the diaphragm and spring.

I got to thinking about that and I agree. I didn't install it. Back to the drawing board, or perhaps I'll just buy an aftermarket one.

[raygreenwood]

You guys re confusing two different parts.

the Bosch part...that was described by the previous poster as used on a Mercedes.....is the same part use on D-jet.

Its purpose has NOTHING whatsoever to do with dampening fuel pressure spikes. It is strictly designed to take away the humming, squealing, whistling sound that is common with early roller cell pumps especially when there are lots of twists and turns within the lines close to the pump on the pressure side....and they work very well.

Its a simple chamber with narrow wall spacing (pancake shaped disc) with offset inlet and outlet. It forces the fuel to swirl in a circle and the vortex dampens the transmitted harmonic of the inlet fuel under pressure.

If you ever ran D-jet in a type 3 or 4 without it....it was a noisey system.

The other "dampener"...some are referring too here...with a spring and diaphragm...is worthwhile as a pulsation damper...but because it flexes on the high spike...and drops pressure...its hideous for maintaining stable fuel pressure.

The other part that some THINK is a dampener...but is not.....is used on CIS injection. Its the fuel pressure accumulator. Its sole purpose is to be a pressure reservoir to keep pressure on the fuel line for a period after shut down to A. prevent evaporation of fuel and vapor lock and B. to aid the system in being closer to design pressure for the injectors on the next start up to make for easier starting.

What pile was mentioning....is that a basic metal diaphragm fuel pressure regulator makes and excellent pulsation dampener....if the dome has enough air volume....and it can be adjusted. The metal diaphragm and spring has a tight uniform rate and can be set to a very small fraction of the actual fuel pressure. This makes the resolution on the pressure swing...very fine and tight...fuel pressure is decently stable.

The best...pressure spike...dampener...I have found....is actually what many refer to as a "swirl pot" (very stupid name that has no description at all of what its actually doing). Its a fuel accumulator with a bleed.

You can make one FAR FAR FAR better than anything you can buy. It has no diaphragm...and no spring...which are actually detrimental. It will both remove air in the lines and insure rock solid stable fuel pressure.

Take a steel or stainless pipe section...maybe 1/2 liter at the smallest. Cap both ends.
Add an inlet barb to the TOP end (supply from the pump)...but not in the cap...put it about 3/4" below the dome in the pipe cap. Then near the bottom...add an outlet barb (to the engine).

The inlet fuel will shed any air in this pipe..which will go upward into the pipe cap dome. The pressure head forces liquid fuel downward where it exits the barb to the engine ring main.

In order to be sure that foam or fine bubble are shed before they can be pushed downward...the volume of this "swirl pot" needs to be about 7-10 seconds of fuel volume time. Because it does not stop to de-aerate...its constantly moving from top to bottom in the swirl pot. If you have any fuel foaming...this separation time is necessary.

So if the pump system is putting out 1 lpm....at say 50 psi....the actual volume FLOW capability will be somewhat higher. Call it 40 ounces per minute. Thats .66 ounces per second passage. So that is about 6-7 ounces roughly of fuel volume....bare minimum.

And...this is just for air separation. If you want PULSATION DAMPENING...double that volume to about 15 ozs (which is just below a half liter).

Volume under pressure in the supply line...as well as distance from the pump= much greater pulsation dampening. This is why all or most of the new Euro cars....especially VAG products....use a main fuel pressure regulator in the filter....waaaay back by the pump to set a higher than necessary main pressure on the line, increase pressure head volume and distance....and then do fine pressure setting at the return line FPR. The fuel pressures are ROCK SOLID...1/2 psi stable on these things.

So how to get separated air out of the dome in the swirl pot? You put a simple screw in orifice whose cross section equates to the flow of one extra injector. You can buy precision screw in micro orifices from places like McMaster Carr supply...pages 522 and 523 or this company http://www.okcc.com/PDF/cat%2011%20Rev%207%2B_web.pdf

You can use a needle valve also. Just plumb that into the return line with a Y fitting. Ray

[MinamiKotaro]

Well, I got this little fellow here.

http://www.amazon.com/gp/product/compat ... f_dp_chart

We'll see what, if any, effect it has on my fuel pressure.

[MinamiKotaro]

[Piledriver]

Looks like a winner...
Perhaps temporarily plumb in through a ball valve so you can A/B test?

[MinamiKotaro]

Initial impressions ...

Oddly enough, the biggest obvious difference is in startup and after start. The Bug idles after cold start without having to be patted and takes gas without stuttering almost immediately. Next most noticeable difference is that it can be lugged down a lot farther without complaining (this includes pulling it down to near-stall in 4th when coming to a stop). I suppose this makes sense, as startup and low-speed/high load would be when the injectors are opening and closing most rapidly and thus most prone to causing fuel pressure fluctuations.

I also took it to about 5000 in 3rd. My AFR was rock steady (though lean) and that DAMNED "burp" that's been there since Day 1 didn't show up at all. I hope that's permanent.

I'm having trouble viewing a datalog (may need to update MegaLog viewer) so my butt-dyno is about all I've got to go on, for now. I think what I've experienced thusfar was definitely worth $22.00.

[thedrew]

sweet! whats the threading of the dampener?