• If you like antique engines, vintage tractors or old iron machinery, register and join us. When you register on Smokstak, please give complete answers and fill in the blanks. - IF YOU ARE ON WIRELESS OR SATELLITE, ENTER YOUR CITY AND STATE! NO ZIPCODES! All registrations are manually approved.

Hydraulic Pressure Switch 50 PSI

jimybuddiesel

Registered
I have a skid steer (New Holland L445 -1982) that has a safety pressure switch that is leaking and need to be replaced.

I would rather not spend 50 dollars for an OEM when there seems to be compatible replacements for 10 dollars available.

I can start a new thread if someone would like to discuss the plus and minus to using OEM versus aftermarket.

The switch I have works great, but leaks. It has leaked for 20 years, but now it is starting to leak too much.

This particular switch is new holland part number 716261. The charge pressure light setting is 50 PSI. This switch has continuity when the engine is not running, once the hydraulic system gets up to pressure, the switch breaks continuity and the dash dummy light turns off.

The replacements I am looking at is 50 PSI, but not sure if it break continuity at that pressure or establish continuity.

ACdelco 8648065 is one part I found. it is a governor switch for a GM TH350C Turbo, which I believe is a transmission.

any detail would be appreciated.
 

Attachments

dalmatiangirl61

Subscriber
Last Subscription Date
07/10/2019
If that is original switch in the pic, it is just a plain pressure switch, so an aftermarket switch should work. NAPA has many of these type switches, their technical support can look up specs on NO/NC and pressure activation points, as these details are not listed in the catalog.

I would also do a search of original P# on ebay, and google to see what is available, needed a similar switch some months ago for Daewoo forklift, napa could get close, but not exact match, found exact match dirt cheap on the net.

The NH P# may or may not match actual P# on that switch, if you can still read# on switch use that in search.
 
Last edited:

jimybuddiesel

Registered
I purchased one from eBay for 9.09, that price included shipping. Once I receive will provide more details.

worried about maximum pressure allowance, this unit has pressure up to 2400 psi. Other issue I detailed in intial post, wether the default has continuity or continuity is established across tabs once 50 psi is reached on the switch.

will also look up Stewart Warner switches to see if I can locate an inexpensive replacement.
 

cornbinder89

Subscriber
Last Subscription Date
05/11/2020
My guess is that only sees charge pump pressure, Hydrostatic piston pumps require positive pressure on them to work. Without the charge pump the hydrostatic pump would fail. You can look up what the charge pump pressure is, but I doubt it is anywhere near 2400 psi. Likley more than 50 but less than 400.
 

jimybuddiesel

Registered
I have purchased a pressure switch that is different than the original and would like to be able to use it with minimal changes to the wiring of my skid steer.

The original switch has continuity between the two points when the pressure is zero, and then the continuity is severed when the switch pressure reaches 50 PSI's. When it reaches 50 PSI;s the dash light and buzzer quit/stop.

The replacement switch is the opposite. When 50 PSI's of pressure is reached, it establishes continuity.

I have attached wiring diagram and photographs of the two switches.

Any details or advice would be appreciated.
 

Attachments

dalmatiangirl61

Subscriber
Last Subscription Date
07/10/2019
The original switch has continuity between the two points when the pressure is zero, and then the continuity is severed when the switch pressure reaches 50 PSI's. When it reaches 50 PSI;s the dash light and buzzer quit/stop.

The replacement switch is the opposite. When 50 PSI's of pressure is reached, it establishes continuity.
I think you will need a different switch. Did you find any part# on the old switch? If so post it and I would gladly search it.
 

jimybuddiesel

Registered
Other than the part number in the parts book. There was not a part number stamped on the switch.

As regards to a relay to "switch" the continuity, I may have a relay in my inventory. I am assuming a basic 12v 30/40 amp SPDT should work. I have a bunch of wiring harnesses from garden tractors.
 

jimybuddiesel

Registered
So, I will have to bring in a 12 volt source?

No way to do it with the ground leg of the connection?

Thank you for taking the time to scetch it out.
 

MColopy

Subscriber
Last Subscription Date
12/14/2019
So, I will have to bring in a 12 volt source?

No way to do it with the ground leg of the connection?

Thank you for taking the time to scetch it out.
Yes you will need to go to the ignition switch and pick a terminal that goes hot when the key is on
 

jimybuddiesel

Registered
Did you find any part# on the old switch? If so post it and I would gladly search it:

Stewart Warner Hobbs part number 25316 also has 50 stamped on it to designate 50 PSI trigger point.

Any details you could provide would be appreciated.

At this point I think I "fixed" it; it was leaking around the crimped edge and I used vice grips to go around the outside and crimp it a bit tighter (The first time after crimping I reinstalled and still leaked a bit, so I repeated the process and it appears to not leak.
First photograph shows how I hooked the unit up to my air line to figure out where it was leaking.

The second photographs shows it leaking (red area).

The final photograph shows how I have it packaged with a baggie and paper towels in case it re-leaks. I have used this method for 20 years to capture the fluid.
 

Attachments

Pete Deets

Subscriber
Last Subscription Date
01/01/2020
The listing says it is an air pressure switch. What would oil do to it?..........PD
 

cornbinder89

Subscriber
Last Subscription Date
05/11/2020
I wouldn't trust it for oil. Oil switches have a small (restricted) opening, if the switch fails, the amount of oil will be less. Air can have a bigger opening and depending on the diaphragm it may or may not be compatible with oil.
You can spend more money trying to save a few buck rather then just ordering the replacement Hobbs switch.
Imagine how much it would cost to re fill the hyd tank after a cheap switch failed during operation and you don't get it shut down in time.
Ask me I know, I once made a mistake and it caused the machine to dump 55 gal of oil in a matter of seconds!
 

cornbinder89

Subscriber
Last Subscription Date
05/11/2020
Another reason oil switches have small orifices is so pump pulsations will not damage the diaphamn, air pressure doesn't hammer even if it is pulsating, it can compress and expand and not transmit the pulse to the switch material.
 

dkamp

eMail NOT Working
I'm surprised that the original(ish) switch had a crimp under system pressure- obviously it was NOT intended for 200+psi operation. Charge pressure doesn't 'live' in a high range, but even WITH pressure relief valves in place, pump action operations can cause spikes that bump 10X at for very short times.
 
Top