Hello, I am trying to restore a Primus 51 that I have had for years. The pump meets a lot of resistance when I try to pressurize the tank. I am familiar with other pressurized camp stoves. Is there a check valve at the end of the pump tube that could be a problem? The leather cup on the pump shaft looks like it is in good condition. When I pump it, a small amount of air enters the tank, but not enough to get much fuel coming out of the orifice and I have to constantly pump to keep the flow going. I put Coleman fuel in the spirit cup and heated up the fuel tubes. It should have fired up in there was enough pressure in the tank, right? Any advice? Thank you.
Welcome to CCS @Ralph Vartabedian There's a non return valve (NRV) at the bottom of the pump tube. It's a spring loaded rubber PIP. Poking a wire down the hole may free up the moving parts but the PIP may have hardened with age and the NRV will need rebuilding. Search the site for NRV and there is plenty of info.
There is a valve at the end of the pump tube- the non-return valve, abbreviated to NRV on this forum. It has a rubber seal, often called the 'pip', which may have stuck, causing excessive resistance. Equally old fuel deposits may be causing the NRV to stick. You can try soaking the valve in light oil or a penetrating oil of your choice, and poking a length of wire through the hole in the NRV body at the bottom of the pump tube, which may physically free it. There is a good chance the rubber pip will have degraded and will no longer provide an adequate seal. In order to replace it, the NRV needs removing and dismantling. Search for 'NRV tool' to see what you need to buy or make. Another cause of pressure loss is the filler cap seal, which may well need replacing.
I'm pretty sure the filler cap is not leaking. It was at first, but I cleaned the rubber seal and ran some 0000 steel wool over the lip of the brass neck. It looks like these replacement parts and tools come from England, which will take a month. I wonder if it is possible to remove the NRV with a socket wrench? I may try that.
@Ralph Vartabedian Hello . Before you do anything with the NRV , is the tank holding pressure ? A few pumps then open the pressure release screw see if it hisses. If it does then check your jet isn’t clogged . You may well have tried this but taking out the NRV without the correct tool can cause major problems . Otherwise follow the good advice from very knowledgeable members written above . Good luck
A socket won't work. The head of the NRV is rectangular in shape and nominally 5mm wide. Some info regarding tools is here but as stated use the search for NRV and you will find a lot of helpful suggestions. An excellent NRV tool Making a special key for NRV removal
I really appreciate the advice I have received here. I ordered a rebuild kit for the No. 51, which includes the NRV removal wrench, and it should arrive by the end of the month. It was advised that I attempt to pressurize the tank and then open up the filler cap or release screw to see if it releases pressure. It did not release any that I could detect. But when I first tried to ignite the stove, I could get enough pressure that the stove momentary ignited, but with liquid, not vaporized, kerosene burning at the orifice. I'm holding off on any other work until the rebuild kit gets here.