I needed to make a hydro pump and I had an idea...
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The key part is a four way refrigeration manifold, of course I don't want to contaminate my good one so a China special is used. This allows for individual valves for refill, vacuum and valves to be used for each side of the suspension - fancy. Refrigeration fittings also allow for easy bleeding of air in the lines - perfect. The pump can be whatever you choose as long as it has a valve to return the fluid to the tank, I used a Chinese clone of a Rothenberger RP50. I would like to enclose the fluid reservoir but I'll probably resort to storing it in a plastic box.
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To me this is a far better than the factory pump where it is a separate hose for vacuum and pressure. There is a dedicated vacuum pump fitting and the "VAC" valve isolates this from the system. It is designed so that when working on a refrigeration system minimal air is introduced. As well as the fitting being able to be hand loosened for bleeding there is also a dedicated valve core which can be depressed for the pump side. Simply press it and pump until fluid comes out.
It is of course optional to be able to connect both sides of the suspension at once but is convenient and reduces the entry of air. I used a four way manifold so that there is a dedicated hose and valve for everything. a cheaper three way manifold could be used however you would have to use one of the gauge ports for vac/refill and have only one output hose or lose some of the benefits. These four way manifolds aren't much more expensive though.
Here's a diagram I just made which should explain it a bit.
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Here are instructions that I wrote. They might appear complicated (just like the factory pump) but it's quite simple once you work out what is happening.
Instructions
Valve "V1" on the RP50 pump can be permanently left open.
To depressurize:
- close VAC valve on manifold
- Connect service fitting/s to vehicle.
- Screw in core depressor/s
- open associated service valve/s on manifold
- open REF valve on manifold
- open V2 on pump
the pressure will drain to the pump reservoir. If you want to dispose of the old fluid you could remove the hose from the pump first and use a bottle.
To evacuate/vacuum and refill
- close REF and VAC valves on manifold
- close V2 on pump
- ensure there is no pressure in pump for safety (release pressure via V2 if needed)
- depress bleed valve on manifold (remove cap). If there is no bleed valve on your manifold loosen the hose.
- gently pump until fluid comes out and then release the bleed valve. The pump side is now free of air.
- Connect service fitting/s to vehicle.
- Screw in core depressor/s
- ensure there is no/low pressure shown on gauges
- close REF valve on manifold
- start vacuum pump
- open VAC valve on manifold only slightly. See Notes
- open applicable service valve/s on manifold
- run vacuum until gauge/s reach desired reading
- close VAC valve on manifold
- stop vacuum pump
- open REF valve on manifold. Fluid will now be drawn into the system.
- pump slowly to desired pressure. Individual service valves can be closed to only increase one side, I would start with both open if both sides are empty.
Increasing pressure when the service fittings have been disconnected
- close REF and VAC valves on manifold
- close V2 on pump
- ensure there is no pressure in pump for safety (release pressure via V2 if needed)
- depress bleed valve on manifold (remove cap). If there is no bleed valve on your manifold loosen the hose.
- gently pump until fluid comes out and then release the bleed valve. The pump side is now free of air.
- Connect service fitting/s to vehicle.
- loosen hose/s on service fittings
- open REF and service valve/s on manifold
- pump until fluid comes out of loose connection/s and tighten.
There is now minimal air in the hoses except for the amount in the coupler.
- Screw in core depressor/s
- pump up to desired pressure.
Disconnecting from vehicle
This procedure is to ensure you don't get sprayed with high pressure fluid.
- Screw out core depressor/s
- open REF and service valve/s on manifold
- open V2 on pump.
Here is a list of required parts:
These are the listings I purchased but give an idea of what to search.
Here's the main components purchased:
Manifold:
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Vacuum pump:
Hand operated pumps etc could be used too but would need adaptors, easier to just get one of these pneumatic ones. They are rubbish for actual aircon work but are mostly fine for this purpose.
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Pressure pump:
Any other suitable pump can also be used.
Typical cheap stuff, listed as 1/4 but was 1/2 bsp.
Schrader Coupling:
One of mine is one of the ones from Airtec and is far better quality. This cheap one I had to file it to allow proper flow. If you can find one with the JIC 37° 7/16-20 UNF male thread then I think it will fit directly to the aircon hoses without an adaptor. The aircon hoses are meant to use a 45° fitting though. I already had one 1/8 NPT one so I bought some adaptors. Although the fitting is restrictive, it isn't as restrictive as the valve core.
Fittings:
1/8 npt female to 1/4 sae flare - hose to schrader coupler
1/2 bsp male to 1/4 sae flare - pump to hose
These are available cheaply on Aliexpress. Some of these fittings are also sold for gas purposes.
Notes
There is one little annoyance with the factory Schrader fittings on the car, specifically the valve cores. They are quite restrictive. The RP50 pump is capable of flowing far more than the fittings can. This means that when pumping the pressure builds up between the pump and coupler then slowly enters the suspension system. This occurs even if the coupler is fitted directly to the pump. The cheaper fitting was horrible so I had to file it for better flow. After some more thought, the valve core is actually the most restrictive part.
This issue exists without the manifold, it is simply to do with the pump. It just means you need to be aware of it when you see the pressure going up high quickly, the system isn't actually at this pressure. As soon as you stop pumping it flows into the system slowly.
Where it is a bit more of an issue is when trying to pull a vacuum. Think about trying to flow what is effectively 14psi through a tiny hole, there won't be much flow before a restriction occurs. This restriction causes the gauges to show a full vacuum however the suspension is not at the same level of vacuum. When the VAC valve is closed the vacuum will equalise. Only opening the VAC valve slightly may make the gauges show a more accurate reading. I hadn't fully worked it out until now so I didn't test it, this explains why the original pumps say to vacuum SLOWLY. Maybe a hand pump is better after all.
Again, these issues are the same whether a refrigeration manifold is used or not. I've seen others say about using a full on electric vacuum pump with no mention of this issue, they probably just never realised. I want to test the actual vacuum in the system properly sometime. I think as long as you vacuum it for a decent length of time it should be good enough, the factory instructions never gave instructions to pull what is called a proper vacuum in refrigeration work. Only opening the VAC valve slightly should give a better indication of the system's vacuum.
After all this I successfully fixed the suspension to the factory height. It's not my mini and it had been sitting low for 5+ years even after being pumped up multiple times by a "professional"
