Manifold Pressure tube/line

[crxcte]

Anyone know where a person can buy a replacement pressure line that runs from the firewall to the intake cyclinder?  Mine is about 24" but really only needs to be about 18".  My line is 1/8" aluminum.

[MARZ]

Your AP can cut and re flare the end of the line to make it fit better - about a  15 minute job 

[crxcte]

Problem is that most flaring tools have the smallest OD of 3/16.  This tubing is 1/8". 

[Shadrach]

Just put a loop in it...

[carusoam]

Be knowledgable about the required vent hole.

 

-a-

[airfoill]

Quote: carusoam

Be knowledgable about the required vent hole.

 

-a-

[carusoam]

Airfoil,

 

The vent hole is a calibrated leak, usually about 2" back from the gauge.

 

This vent allows air to rush back towards the intake side of the cylinder upon shut down.  The gummy build-up of evaporated fuel is kept away from the gauge this way.

 

If the hole is missing, your gauge will be way off at low power settings.

 

Have you had the opportunity to clean the intake side of the engine? Anywhere from the carb, to the intake runners to the valves is full of blue goo.  Fuel injection systems are less susceptible, but the calibrated leak is still required.

 

Best regards,

 

-a-

[carusoam]

Shadrach has good advice,  a simple loop will take up extra length.  Flaring a new tube can be done by hand. Aluminum is quite soft and malleable.  Getting the right diameter vent hole will require the mooney part drawing.  The dimension is only a foot note on one of them.  The drill is quite small.

 

-a-

[Shadrach]

I too am confused about the required vent hole???

All MAP gauges that I know of are sealed aneroid cells.  The outside of the cell is atmospheric and the inside of the cell is plumbed to the manifold. A lever and spindle arrangement linked to a needle or sending unit (depending on whether it's digital or analog) is attached to the aneroid cell. As the cell expands and contracts the movement is transferred mechanically (lever & spindle) or electronically (sending unit) to the needle/readout.... 

[airfoill]

Quote: carusoam

Airfoil,

 

The vent hole is a calibrated leak, usually about 2" back from the gauge.

 

This vent allows air to rush back towards the intake side of the cylinder upon shut down.  The gummy build-up of evaporated fuel is kept away from the gauge this way.

 

If the hole is missing, your gauge will be way off at low power settings.

 

Have you had the opportunity to clean the intake side of the engine? Anywhere from the carb, to the intake runners to the valves is full of blue goo.  Fuel injection systems are less susceptible, but the calibrated leak is still required.

 

Best regards,

 

-a-

[carusoam]

Ross,

 

For electronic manifold pressure, I don't think the vent hole is required.  It would be difficult to pull the blue goo through the copper wire into the gauge.

 

Insert smiley here....

 

-a-

[Shadrach]

-a-

I learn something new everyday. I just built my IO360 up after case crack. It went to the engine shop sans all accessories, and fuel servo. At 880SMOH, there was no "blue goo" in my intake runners nor inside the manifold. In reviewing the MX manual I can find no mention of a hole in the line other than under trouble shooting gauge inaccuracies...  

[Shadrach]

Quote: carusoam

 

Airfoil,

 

The vent hole is a calibrated leak, usually about 2" back from the gauge.

 

This vent allows air to rush back towards the intake side of the cylinder upon shut down.  The gummy build-up of evaporated fuel is kept away

from the gauge this way.

 

If the hole is missing, your gauge will be way off at low power settings.

 

Have you had the opportunity to clean the intake side of the engine? Anywhere from the carb, to the intake runners to the valves is full of blue goo.  Fuel injection systems are less susceptible, but the calibrated leak is still required.

 

Best regards,

 

-a-

 

[carusoam]

Ross,

For you, I will re-iterate a few points.

[1] Your IO-360 is fuel injected.  (As noted above) You have no carburetor, so, no blue goo for you below the injection points.  Your intake tubes should be clean as a whistle.  (where does all the blue dye go...?)

[2] The hole is not about venting the intake system, it is about keeping the mechanical gauge clean of fuel vapor and whatever else can come down the tube from the engine intake (which can include some exhaust by-products as well).

[3] 40 years of conduction and convection of fuel vapors and combustion byproducts can gum up a mechanical gauge unless something is put in the way to keep these materials from entering the gauge.  There is no filter, check valve, or trap.  Vacuum in the gauge at one end is attached to an open ended tube where unwanted things can enter.

Let me present to you a simple method.   A small vent hole located near the gauge, away from the "dirty" intake.  Simple yet ingenious at keeping your gauge from getting the least bit filled up from any unwanted stuff.

You mentioned going to the airport today....Did you find one in your system? 

You may need a mirror and flashlight.  I was able to find the one in my M20C by feel...It had cracked wide open one day (vibration at a stress riser - the hole itself).  Finding the replacement has brought me the knowledge I seek to share in this thread.  Replacing the tube without the hole gives readings that are way off.  Replacing it with the wrong size hole is off as well.  Since power settings and the health of your engine depend on accurate manifold pressure readings, it is somewhat critical to have the proper hole diameter in the tube where it belongs.  The gauge readings are calibrated with having this leak in the line.  For the true engine fanatic, it is time to realize that there is also a micro induction leak into this particular cylinder.

I also learned... The incorrect replacement part that was supplied to me was a 1/4" (rigid) tube.  So, I know some mooneys use a larger diameter tube than the 1/8" in the C.

Best regards,

-a-

[Shadrach]

Thanks for the explanation -a-.

I was confused about this for a few reasons...the biggest being that the OP was wanting to replace or shorten his MP line. Which as you know, is ported to Cyl #3. and runs from there to the firewall fitting.  I did go to the airport and I found no vent forward of the firewall (I did not look behind it). I understand now that it's likely on the backside of the panel and likely just up stream of where the fitting goes into the instrument.  That being said, why does knowledge of this vent hole apply in the OP's situation.  Thanks for bringing me up to speed on this.

Pics attached below...

btw, I did not make a run to the drome just to take pics of a vent line... I was working on the Exec's hangarmate...

[carusoam]

Ross,

 

I may have been unclear about which end the OP had excess.  My line had excess on the cabin side of the fire wall.  If I were to cut it short, I would have lopped off the vent hole.  My tale of caution was to be aware of said hole, if it exists, don't accidentally cut it off.

 

Good news though, by the time I got the right diameter hole drilled into the line, it no longer had the extra loop.... 

 

-a-