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Old 08-14-2019, 01:25 PM
Draker's Avatar
Draker Draker is offline
Join Date: Jun 2016
Location: Livermore, CA
Posts: 314
Default Tip: Dual-circuit pressure switch for Hobbs

Hopefully this helps someone avoid buying the wrong part:

I'm planning on installing a Hobbs meter. The standard way to activate the Hobbs appears to be with an oil pressure-based switch. When oil pressure is present, the switch closes, and the Hobbs meter runs. I'm also planning on running a panel light that is on when the switch is open, indicating low/no oil pressure. For this application, you need a 2 circuit oil pressure switch.

The switch sold by Spruce is Honeywell part number 76575, which is only a single circuit (normally open, suitable for activating the Hobbs meter). The one you'd need to also support a panel light is Honeywell part number 76579, which has dual circuitry: both NO and NC terminals.

Information about these pressure switches can be found in their datasheet:

I obtained mine from eBay, but there are a number of online vendors that sell this part.

Now I've got an extra brand new single-circuit oil pressure switch that I'll either return to Spruce or sell over in the VAF classifieds.
Ryan Drake
Livermore, CA
Donated 12/16/2019
RV-7A: Empennage and wing kits complete minus fiberglass, fuselage 90% complete. Canopy in progress.
N12VD and N23VD reserved... Another decision!

Last edited by Draker : 08-14-2019 at 01:27 PM.
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Old 08-14-2019, 02:09 PM
fl-mike's Avatar
fl-mike fl-mike is offline
Join Date: Jul 2005
Posts: 1,228

The one Van's sells does just what you say.
Oil pressure switch for activating Hour Meter and light IE SPDT PRES-15 SW $35.00
Pressure good = one terminal goes to ground (switch body)
Pressure bad/low = other terminal goes to ground

as long as you use low-side switching, it works.
i.e. +12V ---hobbs---switch---ground
+12V---warning light ---- switch---ground

The Vans part includes a sheet showing how to hook it up.
Mike W
Venice, FL
RV-6A. Mattituck TMX O-360, FP, GRT Sport EFIS, L3 Lynx NGT-9000
N184WM reserved (RV-8)....finishing kit in progress. Titan IOX-370

Last edited by fl-mike : 08-14-2019 at 02:11 PM.
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