Pump rod not seating completely

Discussion in 'Stove Forum' started by Metropolitantrout, Nov 26, 2017.

  1. Metropolitantrout

    Metropolitantrout SotM Winner Subscriber

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    I have an Optimus 00 that I got up and running but the pump rod does not seat completely. It wants to be 1/4' -1/2" up. It's not from a leaky NRV as there is no fuel in the pump tube. It also wants to rise a bit when the fuel cap is removed and the stove is zero pressurized.

    It's not a big deal as the stove runs fine but would like it to fully seat. Any ideas? Jerry
     
  2. hikerduane

    hikerduane Subscriber

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    I have some stoves where the the pump shaft will not go down all the way when using. Spirits of the dead kind causing it to rise when pressure is released? :)
    Duane
     
  3. ArchMc

    ArchMc SotM Winner Subscriber

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    Compressing that last 1/2" of air isn't enough pressure to open the NRV.

    ....Arch
     
  4. Metropolitantrout

    Metropolitantrout SotM Winner Subscriber

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    What do you think changes in the last 1/2" Arch?
     
  5. ArchMc

    ArchMc SotM Winner Subscriber

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    What I meant is that any 1/2" of air in the tube isn't quite enough to move the pip.

    ....Arch
     
  6. cmb56

    cmb56 Sweden Subscriber

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    I have a lot of stoves that do this and I take that as a sign of a good working NRV.

    To make that last compressed air to go into the tank should be with another more loose spring but why should I change that and get a NRV that is less secure?

    Michael
     
  7. tofta

    tofta Subscriber

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    Hi @Metropolitantrout

    I have seen the same with many a stove, never actually speculated too much about it, mostly seen it as a stove personality thing. But, I have noticed different pump designs behave differently, and again the good old leather cup assembly moving on the rod (air passing along the rod) is the best.

    What type of pump does your No 00 have?

    All the best, e
     
  8. kerophile

    kerophile United Kingdom SotM Winner Subscriber

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    Hi, @Metropolitantrout and others.

    This thread describes how the majority of air pumps on classic stoves work:

    https://classiccampstoves.com/threads/typical-pump-assembly.14026/


    The NRV valve opens at about 10psi pressure, and allows air to enter the tank.The pump has to overcome this 10psi, plus any existing pressure in the tank. At the start of pumping this is only the hydrostatic head of the kerosene in the tank. However, as you keep pumping the back-pressure becomes greater. The 10psi NRV pressure setting, at rest, is really there to stop kerosene flowing back into the pump cylinder.

    1. The pump does not fully empty the air cylinder on each stroke as the piston cannot get to the bottom of the cylinder. The head of the NRV protrudes from the base of the cylinder and the piston itself is fitted with a downward-facing pump bucket.

    2. When you stop pumping, the pressure of this pocket of air remaining in the cylinder will be the same as the tank pressure so could be around 2 bar, or approx. 28 psi. This back- pressure will cause the piston to rise, as you have observed, until pressure in the trapped volume equalises to atmospheric pressure. The piston will typically rise an inch (25mm) or so and then stop.

    3. The better the quality of the pump and pump leather, the better the seal, so a rising piston indicates a pump in good condition.

    4. If you want to avoid a rising piston just give the pump rod a “wiggle” from side to side, at the bottom of the pump stoke, when you finish pumping. This usually allows the trapped volume of air to leak past the piston assembly, equalising pressure.

    NOTE. The above remarks apply ONLY to a pump in good condition, with a non-return valve (NRV) which is operating as intended, and not allowing fuel to leak back into the air cylinder.

    If the NRV is leaking and fuel enters the cylinder, the piston can be pushed all the way to the top of the cylinder, and leak fuel out of the pump cap. THIS CAN BE VERY DANGEROUS AS THE FUEL MAY IGNITE AND BURN.

    IF YOU SEE A PUMP ROD RISING OUT OF ITS CYLINDER, MORE THAN AN INCH OR SO, AND CONTINUING TO RISE, RELEASE TANK PRESSURE IMMEDIATELY USING THE AIR-RELEASE VALVE, AND ENSURE THE BURNER IS EXTINGUISHED.


    Trust this helps.
    Best Regards,
    Kerophile.
     
    Last edited by a moderator: Nov 27, 2017
  9. Metropolitantrout

    Metropolitantrout SotM Winner Subscriber

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    @ArchMc
    @hikerduane
    @tofta
    @cmb56
    @kerophile
    @cmb56
    Your combined responses all provided me with good clarification on why it happens, why it's not a big deal and how to possibly remedy it. Thanks fellas!

    Hi Einar, my 00 is a late model, probably from the 60's-70's. I will post some pics.

    Cheers, Jerry
     
  10. MedicineMan4040

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    'RELEASE TANK PRESSURE IMMEDIATELY USING THE AIR-RELEASE VALVE'

    Kerophile, I don't seem to find an air-release valve on my 111B or T :(
     
  11. snwcmpr

    snwcmpr SotM Winner Subscriber

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    @MedicineMan4040
    This topic is about the Optimus 00, a classic kerosene stove with an air release. The 111B and 111T do not have one. To release air on yours ... remove the filler cap WHEN FLAME is OUT.
     
  12. Tony Press

    Tony Press Australia Subscriber

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    @MedicineMan4040

    The Optimus 111 and similar stoves have a positive shut off - the control spindle.

    That means that when the control spindle is closed, the fuel cannot leak (as long as all other seals are working). Therefore you do not need to release pressure in the tank to stop fuel leaking through the jet when the stove is extinguished. Hence, no pressure release.

    On a stove like a Primus No. 1 there is no positive shut off so a pressure release valve is used (it’s also used for regulating pressure while operating).

    Edit: As pointed out by @kerophile releasing pressure on a burning gasoline stove is indeed very dangerous. I think this point was raised here very recently.

    Cheers

    Tony
     
  13. MedicineMan4040

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    Thanks gents. I'm learning....albeit slowly.