Author Topic: Murphy switch  (Read 90 times)

Offline john k

  • Sr. Member
  • ****
  • Posts: 272
Murphy switch
« on: October 31, 2019, 08:41:05 PM »
While out today uh shopping, found an old oil pressure gauge with part of a murphy switch.   Was wondering how many here had experience running machinery with one of these installed?   Heard them called several things, including A hired man switch.  What did you operate ,,,and refer to these as?

Offline skfarmer

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 623
Re: Murphy switch
« Reply #1 on: October 31, 2019, 09:08:02 PM »
New holland combines with 3208 cateepillar engines.
from the ashes shall rise a phoenix

i was here when the hangout turned into mexican food site!

Offline slip knot

  • Hero Member
  • *****
  • Posts: 960
Re: Murphy switch
« Reply #2 on: October 31, 2019, 10:18:23 PM »
I've got a couple of the murphy safety switch gauges. pretty simple concept. They had a setpoint that would ground out the ignition system. They had an adjustable setting so you could adjust the point of ground out. The low oil pressure would normally require a LOP bypass till the pressure came up enough to run. LOP and overtemp were the most common that I've seen. I'll have to get a picture or two of them.

Online gtermini

  • Sr. Member
  • ****
  • Posts: 311
    • Pictures of the junk collection
Re: Murphy switch
« Reply #3 on: October 31, 2019, 11:15:10 PM »
Always called them Murphy switches. Exactly as slip described. Had them on tons of equipment, mostly to combat brain-dead operators. Installed one with oil pressure and water temp on a 4020 that was needed in short order to run a pto irrigation pump 24/7 for about a month. Most engine drive screw compressors will have them factory installed with the override button next to the ignition as well.

Online highland512

  • Sr. Member
  • ****
  • Posts: 416
Re: Murphy switch
« Reply #4 on: November 01, 2019, 09:31:16 AM »
Lots of stationary equipment in construction has them. Screw compressors, large generators, vibratory hammer power packs, and so on. Most of this equipment get turned on in the morning and runs wide open all day by itself with nobody watching it, if it was to develop an oil leak no one would see it until the engine locked up. Murphy switch is cheep protection on very expensive equipment. 

The last one I had on site was on a HPSI power pack with a 3412 V12 caterpillar that powered one of the largest vibratory hammers on the market, the power pack itself is around $200,000.