ARB On-Board High Performance 12 Volt Twin Air Compressor (CKMTA12) install

[Jon Wildsmith]

Jon I'd hate you to think of this as an argument it's more a healthy debate

There was no debate in your previous post Chris, just the assertion I'm wrong and you're right. I'll leave you to it, the question has been asked, it was largely rhetorical, no need to get in a flap about it.

 

[Chris]

Sorry mate absolutely not how it was meant to come over. Certainly not in a flap but typing is difficult whilst driving

I did feel that "why bother?" Was a bit dismissive of the idea. But as I have said many times I take your counsel wisely.

It works for me and that's all I can say. I think or has something to do with the tank being an accumulator that allows the pumps to run in a more efficient part of their curve
But that could be utter tosh.

Chris

 

[clivehorridge]

Whilst trying not to get too entangled in this interesting debate, from simply a practical approach without any calculations, I imagined some 30 minutes before needing to air up, I could switch on my single ARB compressor and fill a tank, say 3 liters or so, to 80 psi which I believe the little pump capable of.

Then, when I need it, I would have a substantial volume of air instantly available at 80 psi which would be at least close to sufficient to fill a flat tyre to say 30 psi in a relatively short time.

at the moment, the pump directly attached to the tyre, takes about 10 to 15 minutes, in the usual crouch position holding the lever, which although doing the job OK, is a bit of a bind.

surely, by this rationale, a fully primed 80 psi receiver would serve to an advantage.

 

[Jon Wildsmith]

I did feel that "why bother?" Was a bit dismissive of the idea.

ok, that wasn't very well put then. It seems like there is an assumption that to have a good on board air system it must have a tank and what I'm asking readers to consider is does that really apply to their requirements any more and not just assume they must have one. You can have hard mounted outlets and pressure switches without a tank, and you can have all those with or without a tank without the compressor being hard mounted as well, which is a related topic.

The capacity of the compressors available these days make me think do we really need tanks? For me the answer is I don't think I'll bother with one again, unless it's because I can

 

[Jon Wildsmith]

Whilst trying not to get too entangled in this interesting debate, from simply a practical approach without any calculations, I imagined some 30 minutes before needing to air up, I could switch on my single ARB compressor and fill a tank, say 3 liters or so, to 80 psi which I believe the little pump capable of.

Then, when I need it, I would have a substantial volume of air instantly available at 80 psi which would be at least close to sufficient to fill a flat tyre to say 30 psi in a relatively short time.

at the moment, the pump directly attached to the tyre, takes about 10 to 15 minutes, in the usual crouch position holding the lever, which although doing the job OK, is a bit of a bind.

surely, by this rationale, a fully primed 80 psi receiver would serve to an advantage.

My view on this Clive is that you'd be better off buying one of the fairly cheap high capacity compressors available now and use that. If you just really like the idea of having a tank that's ok by me, I do/have lots of things on that basis I just think there are other options I'd take.

 

[clivehorridge]

Point taken Jon...

thanks!

 

[Andrew Brierley]

Here's some more food for thought... I have two heavy duty Viair compressors and a 2.5 gallon 150psi tank, and I love the system. Airing up is a breeze (excuse the pun), as is blowing sand out of everywhere. However, I tend to go on group trips, and I'm fully aired up whilst most folks are still on their first wheel. What does that mean??? It means that I then spend more time helping others to air up, so all-in I still spend ages airing up bloomin' tyres!

 

[Geert]

Did all you guys installed and figured out all the connections and wiring and stuff yourselfs?

 

[stumog]

i have a nice compressor i am going to fit to mine my question is this how do you wire up the compressor to turn off at a certan pressure ? where do you get one from? i have a pressure relife valve i fitted put that goes off at 140 psi which i was a bit scared of letting it get to that pressure so i would turn it off before hand. what have you lot done with your systems?

 

[Olazz]

I installed one of these pressure cutoff with solenoid on my system. It cuts out at 10 bar!


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Good for 10,000 cycles alledgedly.

 

[Chris]

Well having been stuck on the M42 for over 3 hours today, I have had some time to think about tanks and not tanks. None of this is science fact. Just thoughts. The first that struck me is that workshop compressors, whilst generally much bigger than our vehicle mounted ones, tend to have tanks. In fact the one at my local fuel station has one, or so it would appear so there must be some kind of case for them. Jon makes a valid observation though in that these portable ones are getting better and better with higher out puts and duty cycles. Part of me asks - why do you want a compressor? Are you going to air up and down - if so how much? Is this simply for tyre maintenance on a long trip? Or are you planning on popping tyres off rims and getting all grubby swapping them over? I think that is really key. I am certainly not advocating a tank for everyone. Nope.

It's also interesting that the ARB set up uses twin pumps. Why is that? They could have just stuck one bigger one in. That made me wonder if Mr Ohm had anything to do with this. I know for sure that if you don't use heavy enough gauge cable on your pump, as the effort goes up, the motors slow and they pull more juice, the cable heats up and the resistance goes .... - well, I mustn't stray out of my comfort zone. But having played around with mine and getting the cable size right, I notice that mine barely slow at all now right up to the point that the tank fills and it cuts off. Or in fact if I am inflating a tyre and drawing that air off. In my mind that means that the pump is running as it should. So lesson one - to get the most out of any pump, it has to be man enough and be supplied with the right juice on demand. Or, effectively it will start to stall. Now, correct me if I am wrong, but that may just actually be a fact.

I have some doubts over the claims of some pumps and I know from conversations that people have shown me some cheap Chinese thing and said 'Look, it does 5 cfm' Yes, it does, but at 0 psi. Ie free running speed. What does it provide when you get up to say 30 psi and the answer has been on some, very little indeed. So your tyre may start off filling very quickly, but those last 10 psi may take an eternity. I guess it's a bit like torque in that respect. That may NOT actually be a fact.

OK. For air to flow into your tyre there has to be a pressure differential. If the tyre is at 35 psi then the supply has to be 35. + X That HAS to be a fact. But, my system has check valves in it (some do not) so if I connect my chuck to a fat tyre and the tank is empty, nothing happens; the tyre doesn't deflate. Some pumps have an open chuck so that when you are not connected to a tyre, they blow air out. I have read on some that you must NOT connect a closed chuck to them as the pressure will build up in the line and inside the compressor, damaging it. Hey, that's what it says on the box. With a pressure switch, all that goes away. Cool.

As the pressure in the tyre goes up the pump has to work harder to maintain that differential until of course the tyre reaches the max pressure of the pump and them it all stops. So tyre is now at 150 psi and pump at the same. Ooer, I hope not. Doesn't particularly safe, but just making the point.

When the pump is pushing directly against the tyre pressure there isn't any flexibility at all. The pump has to overcome the resistance of the tyre pressure and the only thing that can 'give' is pump performance, unless the pump is sufficiently powerful to just keep churning.

But with a tank there is a degree of room that takes up some of that pressure like a buffer so any air not going immediately into the tyre starts to store in the tank even when the chuck is open at the tyre. (experiment coming up later) I seem to remember this would be called an accumulator? Where's the 'hopeful look' emoticon?

On start up with an empty tank my system must reach tyre pressure plus X before anything happens but as I don't start at zero the tank is already tyre + 10X (Tyre at 10 and tank at 150)

As I draw air the pumps replenish that air - the tank doesn't just empty in one go, of course. Now this has to be science fact, as the differential between the pump and they tyre gets closer together ie it's equalising, the transfer of air must also slow down in cc's per second. There will be a formula / graph for each pump somewhere I am sure. Question - with a fixed pump set up, this relationship is effectively preordained. Target pressure, pump characteristics = time to achieve, err yes? The pump curve.

Now what I haven't made clear is that generally I don't run the tank down until the air is effectively passing straight through the tank. I stop and let it build up. I judge this by watching the gauge. As it starts to slow I know I am nearing tyre pressure - whatever it's reached by then, we'll call that 'approach to equalisation'. The pumps now crack on to fill the tank. At this point I KNOW that the tank has effectively become the tyre and should make the pumps groan just as much but it doesn't seem to work quite like that. Maybe it's because the tank isn't rubber and stretching trying to push back and also lift the corner of an 80 series off the ground.

With the tank nearing full again, I pull the trigger, I now have a greater pressure differential to force a higher volume of air into the tyre. Or at least, so I think. Incidentally every time I stop to check the tyre pressure the pumps keep going and gain a bit.

What is in my brain is that if you can have your pumps running at their most efficient air volume producing state things will go more smoothly, you can have a sip of tea and a straighten of your back.

Does any of this matter. No, not one bit. As long as your tyres aren't flat, who cares? It all depends I guess. I like playing, but I'm not the only one.

So, to the laboratory. I have done some timings which probably mean the Sq Root of F* all frankly. But it might get people mulling.

I timed my pump again from empty to switch off. It took 1.15 to fill 2.5 gallon tank to 150 psi. Now it used to be slightly quicker, but I remembered that I have put some new lines on the truck so there is a little more capacity in the system.
Pumps off, open tyre chuck and see how long it took to empty so that there was no discernible air coming out. That took about 55 seconds. So it can empty slightly faster than it can fill. Rough science - I did warn you.

Then, with the tank empty and the chuck open, I clicked the pumps on. At this point, the flow out of the chuck wasn't what I'd call impressive, but it was there. However, as soon as I put my finger over the open end, the pressure rose very quickly indeed until I couldn't close it off. Does that mean that pressure only exists where there is resistance? The pumps never changed note and the gauge was up to 80 psi in seconds. It was an instant build up. I didn't feel that the tank was slowly filling robbing the chuck of pressure.

Then with tank filled and pumps powered up, I opened the chuck again. This time, obviously the pumps kicked back in after 10 seconds or so. I couldn't measure air flow meaningfully, but the blast out of the chuck was pretty huge as you can imagine and even at around 2 mins was still blasting far harder then when the tank started empty and the pumps just blew through.

Right class, conclusions. If you have big tyres that you let down a lot, like to drink tea, chat and smoke a cigar whilst taking a breather then a tank might be a neat toy. You are always producing air, even when fumbling for your lighter and swatting wasps. If you want to get a tyre back on a rim, as we did last Lincomb, then a bigger tank really does work wonders. You can't always work in workshop conditions. If you have air lockers, you don't need a tank, but it does mean that you don't have the pump annoying the hell out of you every time you flick the switch. If you have a portable unit, I can't see why you have a tank frankly. That would be a bit daft.

I can't make the claim that the tank set up is a distinct advantage, but I am pretty certain that it isn't in any way a disadvantage other than cost, space, time fitting it etc. What it has allowed me to do is plumb the two pumps independently into the tank; they aren't T'eed together. Maybe this makes a difference. I did post all of this claptrap a long time ago. I did single hose, twin 6mm hose, single 10mm hose and then twin 10mm hose and the last option was faster. You have to think about duty cycle I guess too. The shorter time your pump runs for and the easier life it has, has to be a good thing. What I can't say is whether bigger is better or in fact is a really small tank a much better bet. I also can't tell you whether you need one. It's for you to decide if you want one.

Wiring it all in isn't difficult. But maybe that should be another thread made into a sticky on the electrical section with some nice drawings. Volunteers?

Chris

 

[clivehorridge]

I suggest Chris, you have a cuppa (and maybe a cigar) and take a breather yourself. In amongst all that lot I recognized some common sense, believe it or not!

I've come to some conclusions (not necessarily the right ones) but conclusions nevertheless. They're in 2 parts, A & B.

A. Use no tank. Nowt more to say on that one, lines direct from the pump. Speed of fill 100% dependent on the performance of the pump.

B. Use a tank. Here's where I think Chris made his point, if I got it right. The pump, lines, tank and the flat tyre are collectively a system, a closed system. Air in a closed system will equalize its pressure, throughout the system. Pressure is not the only important factor, volume is also important. Therefore the combination of volume and pressure when both are high, will give the best results for a speedy rate of fill.

The second important factor I got from Chris' War and Peace, is to permit as rapid a discharge of air as possible. The only sticking point I have with that one is the connection to the tyre valve being a relatively small diameter. Ignoring that for a moment, the lines from the pump (or pumps) to the tank can be relatively small, because the tank can be filled at any rate you want. You can drive the car and the tank will be filling while you're listening to the radio or picking your nose... whatever. Then, when you need air, you have a high volume of high pressure, to do with what you want, so the line(s) to the trigger should be larger than the lines from pump to tank. Then, when you extend the system to a flat tyre, even with the pump off, the tyre will fill assuming the tank volume is equal to 2 x tyre volume and its pressure is sufficiently in excess of the desired pressure of the tyre. Dunno the math, but I would bet someone could come up with some fancy formulae to work it to ideal tank sizes and pressures.

 

[Chris]

Well, I did say I was stuck for 3 hours. Was going to a 10.00 appointment, got there at nearly 14.00. Grr. Oh, another snippet - when I inflate my tyres, I pull the core out. It goes up MUCH faster. Like they do in the tyre shop. That's a winner what ever the set up in my view. But you do need a chuck with a one way valve I'd suggest.

Tolstoy.

 

[Andrew Brierley]

Don't forget to add altitude to the equation.... Try using a standard compressor at, say, 5,000 feet, and notice the difference.....

 

[Bat21]

Pumps now installed and wired in, manifold tank for the lockers valves plumbed in and rear locker valve fitted.

Now onto the tank, yes I have decided to go with a tank

Probably going to go with a 2 gallon one of these but I want to be able to isolate it from the main system so that operating the locker will take seconds rather than have to wait for the large tank to fill. So my plan is to fit one of these on the output port of the manifold tank.

Problem is, I can't find an adapter to enable me to connect a 1/4 BSPT male (the valve) into a 1/4 NPT female (the manifold output port) need to turn it through 90 degrees too

 

[Chris]

Despite what you might think, pressure build up is almost instant Paul. You do not have to build the tank up. With the volume you are producing the tank fills with air very fast and whilst not yet at full pressure it doesn't just sit there building up. It starts trying to escape mediately. One way though to connect bsp to npt is to get two fittings in push fit them connect them with a short piece of air pipe. The push fit ends are universal aren't they. I did that somewhere to connect into the tank iirc. Don't forget that the air locker needs a reduction valve too. They run at 90 psi not 150

Chris

 

[Bat21]

..... Don't forget that the air locker needs a reduction valve too. They run at 90 psi not 150

all the kit was bought from the ARB importers in the Midlands, they never mentioned a reduction valve..... maybe it is built into the actuator valve?

 

[Chris]

Be delighted to be wrong, but my arb blurb was very clear about feeding it with no more than 90 psi. As the compressors run to 150 this was clearly over. So Lil Blue has an adjustable regulator on the bulkhead. There are no other regulating devices that I am aware of. The locker itself doesn't have one and neither does the electric air solenoid. The locker gets what you feed it unless something major has changed OR the compressor only puts out 90 in the first place.

Chris

 

[Andrew Brierley]

Any more than 90psi can blow the seals, so not worth the risk.

all the kit was bought from the ARB importers in the Midlands, they never mentioned a reduction valve..... maybe it is built into the actuator valve?

 

[Bat21]

Any more than 90psi can blow the seals, so not worth the risk.

Not sure where you've pulled that one from, as the original installation guide says they need a minimum of 85psi and a maximum of 105psi

Spoke to ARB this morning and have it first hand from one of their senior tech guys that the CKMTA12 pump is fine for running the lockers:-
Applications include

• Pneumatic supply and electrical control for ARB Air Locker(s). (Air Locker Manifold Kit #171503 required)

The locker manifold kit is the small 'tank' that you can see in the photo.


Features include

• Pressure switch controlled air manifold system regulates pressure between 9.3Bar [135PSI] and 10.3Bar [150PSI] suited to air tools and all ARB Air Locker equipped vehicles.

I have ordered a pressure gauge though to see exactly what psi I'm getting on the output side of the locker solenoid.