Below the pump, at the bottom of the cylinder that the pump moves up and down in, sets a check valve. The check valve allows air to be forced into the fount or tank and, when working properly, stops air from escaping the pressurized fount or tank.
The check valve has two mechanisms that provide this control. The first is a check ball that firmly seats itself closed when there is pressure inside the fount or tank. This check ball becomes unseated (open) when you press the pump downward, or when there is no pressure inside the tank or fount. The "saftey" for the check valve is the tip of the air stem. When you turn the pump shaft clockwise to "close" it screws the air stem into the check valve, thus sealing off the air passage. No air may move into or out of the fount or tank when this operation is done.( See More)
The most likely cause. A build-up of varnish on the check ball and/or seat.
. When a lantern or stove is placed in long-term storage, the combination of air, water, grease and fuel can, over time, form a layer of varnish on the check valve. This varnish will not allow the check ball to fully seat, allowing air to escape out the pump cylinder.
How to repair this problem. First drain all of the fuel from the lantern or stove. Do not re-install the filler cap. Locate the "C" clip around the top cap of the pump (may be small screws) and with a small flat-head screwdriver, gently lift one side of the clip away from the pump and rotate it out, as shown above in Figure 1. If there are screws there, remove them both. Set aside.
Grab the pump and briskly pull it away from the tank or fount. If the aluminum cap will not let go, pry it up with your screwdriver until it is free from the fount or tank. Once you have the pump out, set it aside.
Figure 3 above shows what you will see when you look down the pump shaft at the check valve. The center hole is the air passage and where the check ball sits.
Because we are not going to remove the check valve, the best we can do is to apply cleaner to the check ball and seat. If this does not work, or if you would like information about removing this check valve, please refer to our rebuilding pages.
A very good cleaner to use for the check valve is standard automotive carburetor cleaner. Spray enough down inside the pump cylinder until you can no longer see the check valve and let it sit for five-or-so minutes.
Once this initial soak is complete, drain and repeat once or twice more.
Ensure all of the cleaner is drained from the pump cylinder. Re-install the pump (without air stem) into the cylinder and gently push downward until it bottoms out. Briskly pull the pump upwards then push back down a number of times. This will move the check ball around for additional cleaning.
Spray the carburetor cleaner down the shaft one more time and then drain. Re-install your air stem and the pump. Re-install the fuel filler cap and then give the lantern or stove about 25 good pumps. Even without fuel, you should be able to tell if you have cleaned the check valve sufficiently.
If the check valve is now working, re-install the "C" clip or screws and begin using the appliance. If it does not, try the above steps again. If the check valve is completely shot you may have to replace it. Again, please refer to our rebuilding pages to do this.
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