Sphere Tester, Lack of knowledge showing

[xmexclusive]

Hi All

Putting together a "Noz" style sphere tester.

Realised there are a few things I need to know to get the dimensions right first time.

How powerful does the bottle jack need to be, will a 2 ton one do ok?

I have an unused early XM rear cylinder and the piston seems to be right up at the back end of the bore. Do I leave it like this or do I need to pump it out some way? If so how do I pump it out?

Will I need to restrain the end of the piston rod onto the top of the jack to make sure that it does not knuckle out sideways as the pressure comes on?

When in use do I just fill the top of the cylinder with LHM then screw the sphere to be tested into place?

Anyone know how you test an anti-sink sphere with that unusual thin pipe connection in the centre?

Any help appreciated

John

[kenhall1202]

Hi John,

2 tonne bottle jack is more than adequate.

To test a sphere you only need the piston pulled back no more than 5cm or less from its fully inserted position. Getting the piston moving initially can require a good push due to the 'stiction' of the cylinder seal. After testing a sphere I normally push the piston back with a clean screwdriver. Some sort of spring return on the cylinder would be a useful addition which I have not got round to doing yet on my tester. A small oil top up may be required between successive tests.

No need for side restraint as piston is almost fully inserted during test. The cylinder however must be fully supported on the external machined land.

Yes, just fill the cylinder (only requires a small quantity, say 50ml) and leave a small airspace to avoid LHM spillage when you screw on the sphere. The air bubble compresses and allows a more gradual approach to the sphere pressure as you pump the jack.

Anti sink can be tested in the same way as any other sphere.

One other point - if the pad on the end of of your bottle jack ram is smaller than the internal diameter of the cylinder piston then you might need some sort of adapter so that the jack pushes on the end of the piston rather than disappearing inside it. Might not be required if the fully extended length of the jack ram exceeds the internal length of the suspension cylinder piston. My ancient Dunlop bottle jack has a pad which only just matches the diameter of the BX piston which I used.

Let me know if you require further info - pics of my tester are available in earlier posts.

Regards

Ken

[xmexclusive]

Hi Ken

Thanks for the reply, very helpful, particularly as I did not realise you should be able to move the piston with a bit of force.

Now need to source a suitable gauge having just realised that the one from the junk box is way too low a range for this purpose. Rest of the frame is now made.

Once up and running and have tested the spheres on hand I will need to know about sourcing the modified valves (description, suppliers, quantities and price) also the hoses, gauges and valves.

Then there will be some questions about valves and pipework needed for pressures up to 250psi.

Thanks again

John

[roddew]

Hi John, I recently bought 2 brand new gauges for this purpose from Ebay that were (I think) to 3000 psi. Needless to say they were in the conflagration and I can't recall who I got it from. They were Italian and made from stainless with liquid damping..looked a real quality item and cost me about £6 + post for the two.

Good luck, Rod.

[roddew]

Try Ebay no. 250317789967 Sorry can't get my head round doing you one of those fancy link thingies.


Rodders.

[xmexclusive]

Hi Rod

Thanks, I can manage typing in numbers, links sound difficult. I have just managed to dissable the printer while trying to make the computers talk to the printer over the network. SWMBO is not impressed with my IT skills. Will go into ebay and have a look.

John

[demag]

Err I don't want to appear the compleat dummy here and I understand the mechanics of what you are doing, i.e. screw on sphere, jack up cylinder etc etc. But how do you take your reading on the gauge? Surely if you keep jacking, the reading will keep going up or am I missing the point?

[xmexclusive]

Hi Demag

I am slowly getting this worked out, there is still a lot that I am looking for help on.

If you have a look at Noz's sphere tester write up in the self help he says you quickly reach a point where the jack is effectively stalled and cannot push anymore just maintains its pressure and this gives a steady reading which is the gas pressure in the sphere.

John

This post has been edited by xmexclusive on November 03, 2008 05:21 pm

[kenhall1202]

Heres my explanation.

When you start the test there is a volume of LHM + an air bubble sitting below the sphere neck above the piston. The initial strokes of the jack compress this small air bubble and the gauge pressure rises steadily and fairly quickly (the oil of course is incompressible). The sphere diaphragm remains firmly against the inlet for as long as the bubble pressure is lower than the sphere nitrogen pressure. At the point where the air bubble pressure equals the sphere nitrogen pressure (ie equal pressure on both sides of the diaphragm) the rise in pressure seen on the gauge will appear to level out. This is the sphere charge pressure. Further strokes of the jack will raise the pressure further but only very very slowly because you are now compressing both the bubble and the considerably larger volume of nitrogen in the sphere.

Ken

[xmexclusive]

Hi All

Have reached my next problem. Pipework, the gauge will have an imperial (BSP) thread for the connection. From the cylinder it will be Citroen 3.5mm diameter pipe. What thread and size are these connections and how do I make a LHM tight joint that is good for 100 bar?

John

[Aerodynamica]

This is an interesting idea, I'm keen on building a sphere tester too but I wondered if anyone had any thoughts on the alternate version of the sphere tester that uses a pressure regulator? it measures the volume of LHM it takes to reach cut out which tells you how much LHM it took to reduce the gas volume to the cut out pressure.

I think it uses a HP pump, regulator and a bottle of LHM.

[xmexclusive]

Hi Aero

If you look a Noz's sphere testing self help I think you will also find postings by Shane of his hydraulic pump based tester. There was also one on ebay a few months ago but I got outbid. I just decided that I would build the simpler jack based system first to get testing the 30 or so spare spheres I have to see if any are good. Then I hope to set up to repressurise spheres. If I succeed with that then I will build a pump based system preferably with a 12 volt motor rather than mains so that I can start testing hydraulic components such as the regulators.

John

[kenhall1202]

Hi John

Picture of my gauge connection is attached.

The 3.5mm pipe is soft soldered into the closely matching bore of a high pressure 6mm Swagelock compression fitting (silver solder or brazing would have been better but it hasn't blown apart yet!). The remaining connection is a homemade welded steel 6mm to 3/8" adapter and a 3/8" barrel type connector to the 3/8" gauge connection.
The 1000psi / 70 bar glycerine filled gauge was a cheap eBay buy - if you search there are usually lots of sellers of such gauges as previous posts have already indicated.

Ken