Pump selection for a camp gas geyser





Results 1 to 5 of 5
  1. #1
    Join Date
    Aug 2012
    Location
    Okahandja, Windhoek
    Age
    68
    Posts
    4,439
    Thanked: 852

    Default Pump selection for a camp gas geyser

    Hope someone will benefit from this:


    It was always a bit of struggling with the geysers in both my camper and caravan to set it that you get hot water, let alone at a certain temperature. Eventually I made time to investigate what’s cooking. In both cases the pump was not up to the task. Both geysers are a 5l geyser, not the same make, and both pumps delivered 5 liter per minute (lpm), but only at 20 PSI (pound per square inch) which is the max of the pumps also, which was too low. The one geyser will ignite at only 50 kPa according the sticker on it, but then it needs 12 lpm, the other one requires 1.5 bar minimum pressure. [ 20 PSI = 138 kPa = 1.38 bar].

    So, first thing is to find the minimum demand of the geyser. It will be a certain delivery to the geyser in litter per minute (lpm) at a certain minimum kPa pressure. Usually the geyser is manufactured to supply a certain amount of water at a certain maximum temperature. For example, if it’s a 5l it requires at least 5 lpm of water at a certain minimum pressure else it will not work properly. The geyser also limits the maximum flow to that if the supply is more.

    These geysers have a gas dial and a water dial. With these dials, you can increase or reduce the amount of gas or water supply. To make the flame hotter or colder to increase the water temperature or to make it colder and to increases or reduce the water flow through the geyser to also adjust the water temperature. Thus, you can use both these dials to set the water temperature and supply as you wish. But that is only possible it the water supply is adequate.

    If the water supply and/or pressure is not adequate these dials on the geyser will not be able adjust the geyser properly and you will find it difficult to set the hot water supply as you wish, if at all. Or it will only work at a certain setting and not at any other combination of the dial settings, as in my case.

    All these small DC water pumps has each a unique flow curve, a graph with flow (lpm) vs pressure (PSI or bar or kPa), up to a certain maximum pressure. Delivery reduces as the pressure increases till no delivery, or where the pumps is switched off by the pressure switch.

    Now to select the pump for your geyser you need to check that the pump can deliver at least the minimum flow and pressure required by the geyser. If it’s a 5l geyser you need to make sure that pump can deliver at least that 5l at die minimum pressure required for the geyser. But it’s always better to have the pump to supply a bit more than the minimum required, and to allow for some losses in the plumbing.

    These geysers can take quite a high water pressure, as they are manufactured to take Municipal water supply pressures also. So, you can connect your garden hose pipe to the geyser to see how it supposed to work…, if any issues in an installation.

    All these ‘RV, Camper, Caravan or Marine’ pumps have a either a pressure setting screw and/or a bypass screw.
    The pressure screw and switch, that’s where the wires connect, sets the pressure where the pump will switch off with no flow, in other words when the tap is closed. The pressure builds up in the system let the pressure switch cuts off electricity to the pump motor.

    The bypass screw, elsewhere on the pump body, sets the pressure at which the pumps bypass valve will open to let water circulate in the pump. This allows the pump to run at certain pressures without pressure build up that will stop the pump, as incase with a of lower flow.

    Both these screws can be adjusted to get a smooth flow from the pump. For example, if you open a tap just slightly and the pump starts but stops quit soon after that and start again and continues like that, then you need to adjust it with that said screws. This is called cycling, and you don’t want that. The reason why it’s doing it is that the pressure builds up quickly due to a lower flow and the pressure switch cuts off electricity to the pump motor, and as soon as the pressure drops the switch closes again and the pump starts again. This rapid cycling is not good for the pump. I read somewhere the pump should be at least 3s off at a time? You can then either increase the pressure on the pressure switch that the pump doesn’t switch off so quickly, or not at all, as it will deliver less water at the higher pressure, and/or sets the bypass screw to let some water circulate in the pump that pressure can’t build up high enough to switch off the pump, at that lower flow.

    You always must get a smooth continues flow from the pump over its supply range, but the pressure of the delivery must also be high enough that the geyser operates at all the combinations of water and gas supply.

    Many manufactures use this small noisy 3.5l/m pump which works to a certain as it can pressurize up to 35 PSI, the only issue is that you probably will have to reduce the flow through the geyser to match that supply, else the flame will also goes on and off, or don't ignite.
    Last edited by JLK; 2020/03/06 at 09:04 AM.
    Johan Kriel

  2. The Following User Says Thank You to JLK For This Useful Post:


  3. #2
    Join Date
    Jan 2015
    Location
    Vredenburg
    Age
    42
    Posts
    2,735
    Thanked: 943

    Default Re: Pump selection for a camp gas geyser

    So what pumps do you reccomend?

  4. #3
    Join Date
    Feb 2016
    Location
    Port Elizabeth
    Age
    35
    Posts
    786
    Thanked: 896

    Default Re: Pump selection for a camp gas geyser

    Itís also useful to install a accumulator/expansion tank inline with your system. It is a water chamber which has a pre-pressurized internal air bladder. They are installed in the pressured side of your pump and dampen water pressure 'spikes', which reduce pump cycling, help increse the pump's life and also save a bit of battery power. But note that they only work well with a pump which has a notable difference in cut in and cut out pressure. If your pump switches off at say 22psi, and starts pumping again at 20psi, itís not going to help. If your pump switches off at 40psi and switches on again at 25psi, it helps quite a lot! You will also have to set the pressure inside the accumulator tank to the working pressure of your pump to get it working at optimum levels.

    Here is an example:

    https://parasolsa.co.za/products/a20-expansion-tank

    Name:  IMG_3389.JPG
Views: 144
Size:  180.7 KB

  5. #4
    Join Date
    Feb 2016
    Location
    Port Elizabeth
    Age
    35
    Posts
    786
    Thanked: 896

    Default Re: Pump selection for a camp gas geyser

    Quote Originally Posted by Karoo Klong View Post
    So what pumps do you reccomend?
    Shurflo pumps

    www.sustainable.co.za has a nice range available. And a lot of other toys...

  6. The Following User Says Thank You to MrTolbos For This Useful Post:


  7. #5
    Join Date
    Aug 2012
    Location
    Okahandja, Windhoek
    Age
    68
    Posts
    4,439
    Thanked: 852

    Default Re: Pump selection for a camp gas geyser

    I also use shurflo. Ordered from Seaportsupply, Cape Town. Better priced. And bought the Aqua King Standard. It can pump up to 45 PSI. My geysers work perfect now Cycling easily sorted with the set screws.
    Last edited by JLK; 2020/02/24 at 07:20 AM.
    Johan Kriel

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •