Roll air compressor

[1930]

This roll air compressor runs as quiet as a church mouse when initially started but refuses to start back up as it should once the start up switch detects that the pressure has dropped sufficiently.
When it’s running I can hear air leaking, discovered air leaking back out the air intake tube, difficult for me to even cover tube with my thumb.
Why might this be happening?
Someone suggested an unloader valve?
If this might be the issue how would I find this valve?
It’s an old compressor, manufacturer is just gonna tell me to junk it or take to a repair shop.
It will start fine every time when plugged directly into a power source but when an extension cord is used there is presumably too much of an amperage drop and presumably the electric motor just struggles with trying to spin it over because the cylinder is locked up ( once the air that’s escaping the intake tube lessens in pressure it will start on its own just fine using the extension cord )
If not an unloader valve malfunctioning than why would air be escaping out the intake tube.
Thanks

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[RandyT]

It is kind of a two part system. The unloader valve is what screws into the tank were the pressure line connects from the compressor pump. The small line is the pressure relief line to drain the pressure when the pressure switch reaches correct pressure and shuts off the motor. When the compressor shuts off the unloader valve seals the tank and the line at the pressure switch presses a small button in the end of the copper line/fitting to relieve the pressure for restart. If the compressor is not running and you get back pressure through the pump for a short period then the valve at the pressure switch is not opening. If the pressure is constant to the point of draining the tank then the unloader valve is leaking

 

[1930]

Ok so I need an unloader valve. Thank you
I may post another pict or two for clarification

 

[1930]

Is it safe to assume that this assy is the unloader valve assy? I’ll have to see if it can be purchased separately from the switch if so.

 

[RandyT]

If you need any assistance let me know. I use to be a Rollair service center and still have my parts catalog so I may be able to look up your part numbers if needed.

 

[ray66v]

Though the chance is relatively low, older air compressors are all potential bombs due to tank corrosion from condensate. Especially in portable units, because the also are sometimes subjected to shock during loading, unloading, and transporting.

If you are lucky, the failure will appear in the form of a very slow leak, which is your warning indicator that it's time to replace the tank, or the entire unit.

Using an old compressor in ways that can mitigate injury's in the event of a tank rupture, are relatively simple. Especially, keeping those who don't understand the potential danger involved, completely away from it, anytime the tank has air in it.

 

[1930]

Thank you to everyone that helped me with this compressor. I pulled out the unloader valve, found it stuck, made the repair and now the compressor works flawlessly every time.
I’m going after a heavier duty cord tomm. I hope because I don’t want the compressor sitting outside in the sand, I want it indoors with me out of the elements.
Works fine with the 15 amp cord but I’m gonna get a heavier one anyway cause I don’t want problems down the road.