Hey dudes. I've been wanting/needing a leak-down tester for diagnositics and trouble shooting. Rather than buy one which run upwards of $100 for a good one, Or blow my money on some cheap china stuff, I decided to make my own. They are pretty simple and making my own also helped me understand the reasoning and enginering of these. I made this one today for the sum of about $45 from Lowes. Both gauges move together in a linear fashion and I feel happy with it. The breakdown is this- Gauge (A) Input, Line pressure. Regulator (B)- adjust incoming pressure Orfice tube (C) restrictor/ orfice .040 Gauge (D) Cylinder pressure indicator Quick connect (E) Spark plug line (I used the hose from my compression tester) My question is this. In my version, I placed the inlet/line gauge (A) directly on the regulator. Other ones I have seen place this gauge AFTER the regulator. It makes sense to me, being that the gauge will read line pressure either way. Does anyone see any down side to this? It saves a few bucks on fittings and makes it more compact. Thanks
As long as you are reading the regulated pressure, it's fine. I too built my own. Set the regulated pressure with the outlet not flowing air. I use 100 psi. Then the second gauge gives you % of leakdown when flowing air. For example 90 psi on the second gauge is 10% leakdown. 80 psi is 20%. Very valuable tool.
the first gage should be reporting on regulated pressure on the outlet or discharge port of the regulator, essentially between the regulator and the orifice. i think it would be hard to do otherwise, since I'm not sure I've ever seen a regulator with a port communicating with the "upstream" ( I have would called that inlet) pressure.
Thank you for your post. I have looked at leakdown testers for some time and knew for it to work there had to be some sort of restriction (orifice) in the line. I was never able to find any documentation on what size orifice to use. Is a .040" orifice the standard size for leakdown testers or did you use some method to calculate the orifice size? As far as where to put the inlet pressure gauge; anywhere down stream of the regulator and upstream of the orifice will have the same pressure.
I made one many years ago and estimated the orifice size to be approximately equal to the size of the end gap of the top piston ring. Don't remember what size it was but it was probably around .40 to .100 and no more than 1/16 or 1/8 best I recall. Don't know if the theory made any sense or had relevance but it worked for the motors I was building.
Yes the first gauge is the "regulated" side, not the "tank pressure" so to speak. 51'- I went with the FAA's regulation for piston aircraft of .040 (#60 drill bit)= 1mm. I based mine off of one of our tech's old units. I've found this to be the norm for most all high end test sets as well, So its standard enough for me. I simply filled about 1/2in of the brass tube (C) with J-B Kiwk, then set it on end and let it pool near one side. Once workable, drill one hole through the center and your good to go!. This restrictor is probally the most important part of this. Some cheaper "harbor freight" types use an unsaid size, which may only be "true" when used with their gauges PSI range. some new testers only let you put 15psi into the cylinder, verses the old standard 100 PSI. (I'm sure this is a safety issue to someone ) 100PSI seems more consistant, along with actually giving you audible leak tracing. (i'd have a hard time hearing 15 PSI leaking).
In the United States, FAA specifications[1] state that engines up to 1,000 cu in (16 L) engine displacement require an 0.040 in (1.0 mm) orifice diameter, 0.250 in (6.4 mm) long, 60-degree approach angle. The input pressure is set for 80 psi (550 kPa), and 60 psi (410 kPa) minimum cylinder pressure is the accepted standard.
The Jalopy Journal
