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Thread: canopy problem

  1. #11
    The weight of the roof is not enough to seal the canopy and you want to apply hydraulic pressure to hold it down. Pump running on is normal. If you hold the down button on, the pressure never gets strong enough to hold the roof down.
    Is the relief valve blowing before enough pressure is applied.
    Is the pump producing any downward pressure or just letting fluid out to lower roof. Is it a one way pump.
    Change the up and down pipes and see if it pressures down and nothing upwards etc.

  2. #12
    Senior Member wizrod's Avatar
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    Quote Originally Posted by Gmacz View Post
    If you hold the down button on, the pressure never gets strong enough to hold the roof down.
    No idea. I'll experiment this evening...
    Quote Originally Posted by Gmacz View Post
    Is the relief valve blowing before enough pressure is applied.
    NIO idea, but I guess if it is, its a pump out & rebuild/replace job...?
    Quote Originally Posted by Gmacz View Post
    Is the pump producing any downward pressure or just letting fluid out to lower roof.
    No idea. I'll experiment this evening...
    Quote Originally Posted by Gmacz View Post
    Change the up and down pipes and see if it pressures down and nothing upwards etc.
    Yup.. that's the obvious next experiment....and the potentially messiest!
    cheers

    Paul

  3. #13
    Just remember if taking pipes off the pump, have the roof lowered first! as it gets messy when the weight of the canopy squeezes hydraulic fluid out once the pipes are undone.....made that mistake in the past myself

  4. #14
    Senior Member wizrod's Avatar
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    that's probably as much fun as starting up the engine with a full sump & no oil pressure switch....!!
    cheers

    Paul

  5. #15
    ***Euro-Nova Supporter*** Spacenut's Avatar
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    Hang on a minute, I'm not understanding something here. We are talking about a Smiths Minipack, right? There shouldn't be any noticeable overrun, the motor drives a camshaft which operates a pair of spring loaded reciprocating pistons (on for up, one for down), which in turn blow through disc type non-return valves.

    An adjustable pressure relief valve prevents too much pressure from building up and blowing the seals. The relief pressure can be set as high as 210 bar but I think a typical setting is 110 bar, which if I remember rightly is around 1500 psi. With the motor driven cams acting against that, there will be no overrun, the pump will stop pretty quickly.

    Also, the Smiths Minipack is the king of negative holding pressure! In good condition the canopy will stay open for months without sinking - so with the canopy closed you should not have been able to lift it against the hydraulic pressure. I think Gmacz may have a point about the pressure relief valve. There are some Smiths Hydraulics leaflets on setting up the Minipack in some of the older versions of the Modifications & Service manual, if you have a copy. Might be worth looking into. If the relief valve is faulty or maladjusted that may also explain how the small amount of inertia in the motor armature can lead to overrun - there is no hydraulic resistance to work against.

    Failing that, the seals in the rams themselves may be suspect - in the whole hydraulic system, it is these that suffer most from wear. I got about 6 years use out of mine before I had to replace them, which I think is pretty typical.

    Lauren
    only Pythagoras can save me now!

  6. #16
    I was just being general about hyd pumps.
    Hydraulics and hydrostatic systems are a decent part of what i usually do.
    Never seen a smiths pump or any tech on it.
    Spacenut is the one for this problem.

  7. #17
    ***Euro-Nova Supporter***
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    Quote Originally Posted by wizrod View Post
    I think you have misunderstood me. When I said the motor runs on briefly, I meant that once the power to the motor is shut off, it doesn't stop dead, but takes a short time to wind down due to the momentum of the rotating parts in the motor.

    Power to the motor is controlled by a Lucas starter relay, which in turn is controlled by a pair of standard 30A automotive relays - one each for Up & Down, plus a 30A relay each for the 2 valves in the pump. I've tested each individually & they all work fine.

    TBH, I've had this problem issue since I've had the car - (& I've renewed all the electrical controls since then). In fact, I once had to squeeze out of the car by pushing the roof up by hand - I could never have done this if it was held down under pressure, so I think its a fair bet that the pump is where the problem lies...

    P.
    So my point here is that you have cut the power to the Lucas Starter relay, not the Motor, and I am suggesting that the Lucas relay is slow to release, which gives you your overrun, and the difference in operating time of the Lucas relay vs the mini-pack valves, gives you the small change of direction you experience when you close the roof. My Nova had a mini-pack and I had exactly this problem.

    As suggested above, a working mini-pack doesn't overrun, it stops on a sixpence when you cut the power, so there is a problem there somewhere.

    I would change-out the Lucas relay if you have not already done so, but I wouldn't worry to much about it, because your *real* problem is that you can push your roof up manually, i.e. it holds UP but not DOWN, so it's likely that the respective valve on your minipack is leaking (not the Rams themselves), so yeah, you will have to pull your mini-pack apart after all; I don't envy you that task.

  8. #18

  9. #19
    Senior Member wizrod's Avatar
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    Thanks again for your input.

    I don't think the problem is the Lucas relay - it makes a fairly loud 'thunk' when it opens or closes and I definitely hear it in conjunction to the observed over-run. In addition there is the observed difference between stopping the roof part way & part way down:
    • Stopping part way down: when I release the switch I hear the Lucas relay's thunk and the roof stops moving immediately & abruptly.
    • Stopping part way up: when I release the switch I hear the Lucas relay's thunk, but the roof continues to list for (maybe) a second or so. During this time the pitch of the motor is audibly declining, as it is slowing.


    I think that if the relay sticking were the cause of the problem, then just I'd see a brief delay in stopping, but it would still stop abruptly.

    Sooo... (re-)reviewing the posted Mini-pack pages (Thanks David) and trying to recall my O-Level Technology lesson on Hydraulic circuit symbology, I think what is happening is that the valves are normally closed (when un-energised), so containing the oil pressure in the rams & the pump. When a value opens, a path to the oil reservoir is opened (as when one of the pressure relief valves open).

    So, in my case (in the example of the 'Double acting circuit with breakaway relief valve Option):
    • When I operate the Up switch:
      • The pump pumps
      • Valve B is closed, so oil is pushed in to the bottom of the ram
      • Valve A is open, so oil pushed out of the top of the ram returns to the reservoir.

    • When I release the Up switch:
      • power is cut to the motor.
      • Valve B remains closed (so the roof stays open).
      • Valve A remains open (or the pressure relief valve is stuck open), so oil can still be pushed out of the top of the ram (and back to the reservoir), as the pump winds down, so the ram continues to rise.


    I haven't tested this, but I think that if I were to just run the pump, the roof would raise without touching the valves.

    So....either Valve A is stuck open...or the pressure relief valve on Valve A's side is stuck open. (Also, I'm not sure if I have the 'Optional' pressure relief valves)

    How can I test this? My pump is wrapped in sound deadening wrap, but if I were to unwrap it, would the operation of the valve generate an audible click? If so, I assume I'd hear a click for Valve B, but not for Valve A...? Even swapping the Up pipes for Down (as Gmacz suggested), I wouldn't be able to determine if it were a sticking valve OR pressure relief valve that is to blame.

    In reality though, since both the electric valves the pressure relief valves are integral components to the pump unit as a whole (and from this user's point of view at least) not user serviceable the only real option is removal & repair/replacement of the whole thing...?

    ...or am I missing a point somewhere!?

    At the very least, I'll unwrap the the pump this evening, try to see & decode the ID, look for the pressure relief valves (and their adjustment screws) & explicitly test the valves (as opposed to relying on the relays).

    P.
    cheers

    Paul

  10. #20
    Senior Member MicksRedNova's Avatar
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    Paul
    Yes, the solenoid valves make an audible click when operating. You can energise them without the pump running by taking a wire off the Lucas solenoid.
    . If you operate the pump without energising either valve it pumps to nowhere until the relief valve triggers.
    I suspect your down valve is not operating correctly, it has two functions. One holds the pressure in the circuit the other allows fluid to flow back to the resevoir from the 'up' circuit. The flow back seems to be working, otherwise your roof would be jammed up. But the pressure hold part is not working, normally when you take power off the valve it snaps shut and your roof stops dead, whichever way its travelling.

    I think the valves/solenoids in the pump are accessible. I believe Alex had his apart (which I've now got) but I don't know how difficult it is, or whether parts are available. I have a spare pump available (untested) but I think Alex said it was working, if you need it.

    Its possible yours is just jammed up with crud.

    Mick
    Club Nova Member (F-036)

    MicksRedNova2 may take as long as the original!!

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