# Old Furnas Style H1 Presuure Switch



## HarryM (Nov 4, 2021)

I need a replacement for a Furnas Style H1 pressure switch. This is from an air compressor used in a gas station circa 1955.
It's a two stage on the top of a 200psi tank. The switch has a 5/8 thread on the bottom and the motor is 3HP 220V. I run the compressor at 120-140 psi.
OR I could make a new diaphram.


----------



## iowagold (Jan 22, 2020)

just key that info in on the search on amazon.
snap a few pix of what you have and post them please.


----------



## stevon (Mar 5, 2019)

HarryM,

The question I would ask is how many amps does the motor require to run at full load. The old electric motors are not always the most efficient designs and draw a lot more current than modern efficient designs. An older 3 HP electric motor can draw up to 20 amps or more at 230 volts. This would be at the extreme limit of most pressure switches ability to start it. A magnetic starter would be recommended for any motors that draw over 15 FLA. The problem is the motor's LRA (locked rotor amps) for a second when first turned on under load at 0 rpm. Your motor can draw 100 amps or more on startup, that's why pressure switches and relays in general are rated in HP of the motor load it is controlling and not just in amps. Do you have an ammeter? a $15 dollar Harbor Freight one would do

Stephen



HarryM said:


> I need a replacement for a Furnas Style H1 pressure switch. This is from an air compressor used in a gas station circa 1955.
> It's a two stage on the top of a 200psi tank. The switch has a 5/8 thread on the bottom and the motor is 3HP 220V. I run the compressor at 120-140 psi.
> OR I could make a new diaphram.


----------

