Pressure Switch

[Mark L]

This is a question I had this week concerning a pressure switch that I ask of Teledyne Mattituck (where I purchased my engine). I though it might be of interest to the group.

Question: Last summer I bought a TMX-IO360 from Teledyne Mattituck. I am now installing on my RV-7. My question: I plan on putting a low pressure warning light on my panel. Would you recommend 15, 35, or 50 psi for this purpose? Or, would you recommend something different: What would be considered red zone, yellow zone, normal? I also plan to use this for my hobbs.

Answer: The oil pressure at idle with hot oil will be less then minimum cruise desired oil pressure. If you want the light to illuminate in cruise when you have less then desire oil pressure then use one the goes off in the area of 50psi as 55 psi is min cruise oil pressure. However using this setting will have the light illuminated for all operation at or near idle with hot oil. So the light would be on a lot when there wasn't a problem and the hobbs would only run when the OP was above 50psi. using this setting you would be warned of oil pressures in flight that were dangerous. Min idle oil pressure is 25 psi so if you want the light to illuminate for less the desirable oil pressure at idle speed then use 20 psi switch. With that Hobbs will work when ever light is off and that should be 99.9% of the time but it will only signal the light in cruise operation when the pressure is way below minimum desired cruise oil pressure and the possibility of engine damage exists without the light being illuminated, at cruise power settings.

Oil pressure limts are as follows:
Min Ilde 25 psi (bottom red line with yellow arch to 55 psi)
Desired cruise oil pressure with hot oil is 55psi to 95 psi with it nornally set for 70-80psi( green arch 55-95 with yellow 25-55 and 95-115)
Max oil pressure is 115 psi ( top red line)
If you want the light to go on at undesirable cruise oil pressures then I would think that you might want to use two switches one for OP and one for hobbs.
If you just want below min idle illumination, then you could use one switch for both Hobbs and light.

Good Luck,
Mahlon
Mattituck Services Inc.

These guys have been the best. I think I will try to use a stewart warner, 3-terminal switch @ 35 psi. I think this may hit the spot.

[Wayne Gillispie]

So no oil pressure switch on mine.