A2Jake

A2Jake

Active Member
Im am looking for a source and maybe by chance the number for the "SENDER" to activate an panel mount light for low oil pressure. Yes, most automotive senders will work but I would really prefer to find the SENDER used on a Certified Aircraft. Im not familiar with which, if any had this light and sender combination installed from the manufacture i.e.. Cessna, Piper, etc.
Thanks
 
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every unit i have seen on a certified aircraft is nothing more than an overpriced automotive part. go to a good napa auto parts (they are the only one I know of that still has a catalog rack) and tell them what pressure you want if it needs to be normally open or normally closed. they can spec it by that.

bob burns
RV-4
N82RB RV-4
 
I agree, you won't be getting a better product by buying certified aviation part in this case.
 
just use the other pole of the oil pressure switch used for the Hobbs meter. The Hobbs pole turns ON when there is oil pressure, the other pole turns ON when there is low oil pressure.
 
fl-mike said:
just use the other pole of the oil pressure switch used for the Hobbs meter. The Hobbs pole turns ON when there is oil pressure, the other pole turns ON when there is low oil pressure.
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I did the same. I used the pressure switch from acs. One side for the hobbs, the other for the light. Since the two devices are on separate busses. The switch goes to ground rather than to a hot buss.
 
That's a 4 PSI switch. Lycoming oil pressure ideally runs about 60 PSI in flight, so 4 PSI would be much to low to give any meaningful warning?
 
Just ordered the 10 psi

digidocs said:
It looks like many of the certified switches are made by Springfield/Honeywell.

The link below points to a PDF catalog of these switches with a range of set points from 0.5-150psi. Once you have the part number you'd like, you could order from a Allied Electronics or a variety of other sources.

https://www.alliedelec.com/Images/P..._INC/HOBBS-INC_INDUSTRIAL-CONTROL_6110009.PDF

Hope that helps,
David
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Thank You David,
This is EXACTLY what I was looking for, Just ordered 2 from Allied Electronics,
1 for my Jacobs (round engine :D ) and 1 for the Flat engine in my RV-8.

Thank You to "everyone" who replied
Jared
 
fl-mike said:
Okay. Please define "low", then we can work from that.
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a 4 PSI switch is fine for this application. This is an Idiot light designed to warn of no pressure, which is the failure point requiring immediate attention. An oil pressure gauge should be used for monitoring running oil pressure and it will identify troubles brewing with your oil pressure. In my experience in automotive (typical oil pressures of 50-60 PSI), you either have normal to low (50-20 PSI) pressure (various causes for the deviation) or no oil pressure from catostrophic failure. I cannot imagine a scenario that would have 5 PSI for more than a couple of seconds on it's way to 0. Further, I believe Lycoming specifies acceptable idle level oil pressure down to 20 PSI. This pressure should concern you as to why, but IMHO, should not flash the disaster light.

In the end, it really depends on your reason for having the light. 30 PSI is quite low for 3500 RPM, but may be perfectly normal for idle. You're not going to find an idiot light to cover this scenario. You need a gauge for this.

Larry
 
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lr172 said:
a 4 PSI switch is fine for this application. This is an Idiot light designed to warn of no pressure, which is the failure point requiring immediate attention. An oil pressure gauge should be used for monitoring running oil pressure and it will identify troubles brewing with your oil pressure. In my experience in automotive (typical oil pressures of 50-60 PSI), you either have normal to low (50-20 PSI) pressure (various causes for the deviation) or no oil pressure from catostrophic failure. I cannot imagine a scenario that would have 5 PSI for more than a couple of seconds on it's way to 0. Further, I believe Lycoming specifies acceptable idle level oil pressure down to 20 PSI. This pressure should concern you as to why, but IMHO, should not flash the disaster light.

In the end, it really depends on your reason for having the light. 30 PSI is quite low for 3500 RPM, but may be perfectly normal for idle. You're not going to find an idiot light to cover this scenario. You need a gauge for this.

Larry
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Good Summary - Think of the oil system as a fixed displacement pump pushing oil through an orifice. The pressure will climb with rpm until the oil bypass (may be called pressure regulator) releases and causes a break in the RPM vs Pressure curve. Lower fluid viscosity will result in a displacement of that curve to a lower pressure, but the same profile. So - oil temperature and oil type affect this curve. Additionally, each engine has a slightly different equivalent orifice.

The primary need for oil pressure is to push oil through the bearings and keep them cool. Hydrodynamic forces keep the parts separated. The system is designed to have excess oil flow, and it has a minimum oil-to-bearing pressure requirement. During full load that could be 25 psi.

The 4 psi switch is for a low idle, hot oil, low viscosity condition where the curve has dropped so low as to provide less than 4 psi at idle. If the light comes on just before shutdown on a hot engine, this is the only condition in which this switch can give a relatively accurate condition of the system.

Knowing what your gage reads with 180F oil, at some RPM when flying is a much better indication of your systems health. Again, other than low rpm hot idle, it will not provide a useful function.
 
Light and Switch

I use a NC/NO pressure switch (purchased from Aircraft Spruce). It is connected to my Hobbs (yes I still like a separate Hobbs) and a very sunlight visible LED light. (http://www.vansairforce.com/community/showthread.php?p=357950&highlight=light#post357950).

The light serves two purposes; a low oil pressure warning and a master reminder light.

If the master switch is on and the engine isn?t running the light is on. So it serves as a master reminder light. It is very visible even in the brightest sunlight.

When I start the engine the light should go out within a few seconds. If it is a cold morning (yes we have cold mornings in Tucson) I typically count the seconds until the light goes out. If it doesn?t go out within 7-10 seconds something is very wrong and I will shut the engine off (this has never happened).

This setup works great and has helped prevent me from leaving the master on accidently. I would install it the same way if I build another airplane and would recommend this setup to any RV builder.
 
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