How to replace control knob o ring on pancake compressor EC-510 model

So the first (most obvious but sometimes overlooked) thing - check to make sure the tank drains are closed.
Listen for a leak at the pressure switch - it will continue to leak after the compressor shuts off. If this is the case then you need a check valve (Part # 53A on the breakdown)
If it builds pressure but not enough to shut off and there are no leaks I would look at the valves located in the head (Part # 14 on the breakdown) - piston rings are not a normal failure part on this model but could also cause this.

first control non return check valve on the tank second the hose connections and pressure line tirth cilinder membrane or piston ring worn if an oilless compressor Usually under pressure control a pressure reliever which must be forced out of pressure, it may be that the pressure gauge does not close off

If your quick coupler is not jammed up, (remove & test) and assuming you are pulling the regulator knob out to adjust the pressure and it is not stripped, you will need a new manifold kit.
There are about 6 versions of this unit so you will need model and type to get the correct part. There are no individual regulator parts available for this unit.

check air tank drain valve located on bottom of tank, if it is not leaking try adjusting air pres regulator (large black knob close to air hose connection.) the knob when turned in will increase the tank air pressure, if knob wont turn check that lock ring on bottom of knob to make sure it is disengaged. also check for air leaks in all lines and connections

If your compressor keeps running and only builds to 25psi, I would suspect the reed valves, head gaskets or a leak. With the compressor running spray soapy water on all fittings, around the head area and tank components. If no leak is found, remove the air filter and feel for suction at the intake(make sure head is not too hot). If you feel good suction at first then suction is lost after reaching 25 psi, most likely reeds or gaskets (with bad reed valves, sometimes you will actually feel air blowing out of the intake). Good luck

Small leak will prevent the unit from building proper pressure. Check all connections with soapy water and repair as needed (including under cover). If no leaks are found check cylinder for scratches. Push piston to top of stroke and check walls for fine scratches. If scratched, pressure is leaking past vinyl piston ring. If no scratches or leaks, most likely reed valves, head gasket or combination of both. Easy test, with compressor running and attained 90 lbs, place finger over air intake and check for good suction (carefull could be hot) . If good suction, then air is leaking somewhere, of no suction suspect reed valves/worn cylinder, if air seems to be blowing out of intake, suspect reeds /gaskets. Good holidays

I dont know if it is like mine,but if you can let the air out of it and remove the regulator knob,and it`s components,you may can set it to just to be open all the time,in other words,by pass the control knob valve.Shout back at me if I can help.

I am assuming that your compressor is oilfree type. Lets go over some basics to determine where fault is located. You will need to do some simple tests. If there are leaks the compressor may not reach set pressure. I use soapy water on all connections and on the head/headvalve (remove plastic covers to get to all parts that may leak) while compressor is running. Make repairs as necessary. If still low pressure, while compressor is running and has reached max obtainable pressure (in your case 15 lbs), carefully place finger over intake port hole (remove filter). If the compressor is pumping normally but leaking there will be ample suction at intake and cause the compressor to speed-up when intake is obstructed with finger. If you feel plenty of suction and no visible (soapy water) leaks, then the problem is probably the cylinder /ring is not correctly seating /scratched and air is leaking past cylinder. Make sure that the cylinder /piston ring is properly aligned and that the lip on the vinyl ring is up toward the head. On oilfree compressors you can examine the cylinder by pushing the piston all the way up, then look for scratches neer top of cylinder. If scratched install cylinder kit. If you do not feel suction but rather air blowing out of the intake, then the problem is the headvalve plate/reed valves are leaking. The reeds must seal perfectly on their seats and not be bent or have obstruction. Replace as necessary. Only one other thing to check and that is the intank check valve. Easy to check. Run compressor till you have about 15 + lbs in the tank then unplug compressor. Carefully loosen the inlet hose at checkvalve and listen for air leaking out of tank. If leaking replace checkvalve. Use caution when removing head to try and save the gaskets. If you see any model numbers on your compressor beginning with WL, you probably have a unit built by Campbell Hausfeld and can find parts at www.chpower.com
Good luck on your repair and email if you have other question.

Don"t worry, even the best techs overlook a thing or two during repairs. Lets go over some basics to determine where fault is located. You will need to do some simple tests. If there are leaks the compressor may not reach set pressure. I use soapy water on all connections and on the head/headvalve while compressor is running. Make repairs as necessary. If still low pressure, while compressor is running and has reached max obtainable pressure (still low 70 - 80 lbs), carefully place finger over intake port hole (remove filter). If the compressor is pumping normally but leaking there will be ample suction at intake and cause the compressor to speed-up when intake is obstructed with finger. If you feel plenty of suction and no visible (soapy water) leaks, then the problem is probably the cylinder /ring is not correctly seating and air is leaking past cylinder. Make sure that the cylinder /piston ring is properly alighed and that the lip on the vinyl ring is up toward the head. If you do not feel suction but rather air seeming blowing out of the intake, then the problem is the headvalve plate/reed valves are leaking. The reeds must seal perfectly on their seats and not bent or have obstruction. Replace as necessary. Only one other thing to check and that is the intank check valve. Easy to check. Run compressor till you have about 70 lbs in the tank then unplug compressor. Carefully loosen the inlet hose at checkvalve and listen for air leaking out of tank. If leaking replace checkvalve. Use caution when removing head to try and save the gaskets. Good luck on your repair and email if you have other question.

Typically on the inside cover of the electical box it will illustrate the cut-in/cut-out controls. There should also be a fill port above the pump end of the compressor. Do you have a sight glass on the side of the compressor *(around the area of the leaking oil) usually if its coming out its due to overfilling or tipping over of the compressor.