OBA pressure switch location

I'm rebuilding my OBA setup in preparation for my 4.88s and ARBs. I trying to clean up the setup and make more space for my manifold for the solenoids. Any reason why I shouldn't replace the gauge on my compressor with my Viair switch? The gauge jumps too much to be useful when the compressor is on. I'll add a small gauge elsewhere. Are the spikes in pressure from the compressor cylinder going to make the switch angry? I'm sure down the line the pressure is more stable. I'm going to add a gauge on my manifold after the pressure has been regulated to 90psi.
Thanks for any input.

 

That location will be fine. FWIW that compressor already has a 30A relay inside.
Some space could be saved by using one of the tiny (non relay) switches. Also the cylinder head can be rotated to help optimize plumbing lay out and extra ports can be added (drill and tap).

Then there is the near endless list of low buck performance/longevity/bling upgrades for the MV50 and it's variants. I have a long ass write up on all of them as done to the "Top Fuel" unit below if you want it and have lots of time on your hands.


Relay

 

Glad someone replied. I got antsy and mounted it. Guess I have two relays now. As it stands I have just enough room with the switch there. I like reading so shoot me the link to your write up. Thanks!

 

You asked for it.
This write up was done about 5 years ago. I now have CO2 but find myself still using this thing because it is small and light.
These days there are quite a few other affordable options out there.

HERE WE GO


First, all this stuff is about a 3 year old Harbor Freight and a new (Jan 09) Master Flow 1050 Tsunami. The MF1050 has quite a few similar variants. The current HF unit is not worth fooling with.

Long story short, the best mods, (if you have any kind of other life) is to re-wire the thing and open up the ports. Everything else I did had minimal performance gains other than longevity.
I would not recommend these things for any more than filling up to 33" tires as performance drops off rapidly over 40psi. They will go to 150 and beyond but at great cost in time and risk of melting the Polar Icecap.

Testing was done as follows: 4900' elevation, room temp (68 deg or so), powered from running truck/Optima, filling a 3.5 gal tank from 0-105psi and the most useful 0-40psi.
3 stages of development were tested in this manner, stock, with wiring and porting, and finally with "the works".

Results: 0-40psi, stock 56 seconds, with wire and porting 42 sec, all mods 37 sec.
Results: 0-105psi, stock 3min 38 sec, with wire and porting 3min 21 sec, all mods 3 min 15 sec.

This shows that most of the gains were in the "tire inflation" zone. If you want to keep a decent size tank filled and use air tools, these things are not the answer. Get a $200 Puma, divorce the tank, pump, controls, and be done.
On the 1050 I run an 85psi on, 105psi off Viar pressure switch. This allows the use of a 10' power cable and a coiled hose/standard fittings without having to manually turn the thing on and off all the time while I check the tire pressure. Just pull off the tire chuck, the compressor pressurizes the hose to 105psi (in about 2 sec) and shuts off.

Here is the play by play.
Steps may not be in chronological order.

14g stock wire and 12g "Low Voltage Underground Landscape Lighting Wire" sold by the foot here at Lowes @ $0.56/foot


Ditch the fuse holder and replace with a quality one or better yet a $4 30a ckt breaker. Check all connections and re-solder any thing that looks weak. I was able to cram it all inside the end bell including the breaker. The relay will want to short against the end cap of the motor. I arranged the wires to lay between the two.


The surfaced head showing the opened up intake and exhaust ports. I left a thin web of material to help support a lighter thinner and flatter intake reed valve made from .003 feeler gauge stock. Look how crude the .006" stock reed looks compared to the .003" gauge stock. Looks like it was cut from a tin can with snips. Red Loctite on the reed screws is good. The intake provided by far the biggest gain of the two.


Head with beautiful new reed.


Intake and exhaust ports on the outer part of the head drilled and tapped to accept 1/4" NPT manifolding and fittings, "color matched" of course. Drill out any pipe fittings used on the intake side to the id of the 1/4" piping, makes a difference.


This is a HF unit with the head jacked up showing the piston with its dual (riveted in place) intake reeds. I'm working on porting that baby now.


After testing the thing worked great but the 1050 motor would not restart against a head of any more than 30psi. It just buzzed and made the cables get real hot. Apart came the motor. I found the plastic brush holder warped due to the thermal cut out switch being jammed underneath. That’s how they built it. That put the brushes at an angle to the commutator, not good. I put the 1050 motor away for now and planned to swap in the HF motor.


The HF motor suffered from the same thing (bent brush holder) and the armature was different leaving 2/3 of the brush hanging out over the end of the commutator. The solution was to install 5/16" stand offs under the holder and add two more mounting bolts to draw the holder parallel to the motor end plate. The thermal cut out switch was ditched in favor of the "feel it and see if it's hot" method.


The 3 year old brushes had scored the commutator so on to the baby lathe for a re-cut, like new.


At this point, a picture is worth a thousand words, what a mess.


At this point the differences between the 1050 and the HF were really adding up. Although from a distance things like the castings look identical, they are not. The HF motor makes the 1050 look like a toy. It has stronger magnets, better ball bearings, the armature had nice tight windings, there were the proper high dielectric insulators on the armature polls, a .1uf capacitor across the motor leads (cuts down arcing of the brushes) and the can was some kind of seamless tube that had been finished up on a lathe.
The bore and stroke of both are the same and the pistons are interchangeable.
In both units the crank throw was not inline with the cylinder. This caused a good bit of binding of the piston/cylinder on the 1050. It took 5/32" spacers between the motor (HF) and crankcase (1050) to get it right.
Finally, the HF heat sink was a light interference fit with the cylinder sleeve and had 360 degree contact while the 1050 (left) had 4 little bosses only allowing minimal contact. The 1050 heat sink is mostly just there to hold the head up. I used the HF heat sink in the "Frankencompressor".


The final hybrid after proper painting, addition of a check valve and yes, the tips of the fins have been wet sanded to bright metal. Alert the Mall!


And another


The test rig


One final observation. From to about 0-35psi these things really shine for the money. Above that they just don't have the displacement to be of much good. I have read posts that claim 2.5 cfm @90psi, it just isn’t so. I would respectfully question the accuracy and method of their testing.
One more thing, I promise it's the last one, I ran a 0-30 psi test and it only took 24 seconds.

 

I guess I'll start by rewiring this little thing. Since my pressure switch has a relay I'm assuming I can simplify things and do away with the internal relay? I'll run the the dash switch in series through the switch on the compressor so I can still turn it off under the hood without the internal relay.

 

That will be fine, I sense you know what you are doing. If I had to guess, the Viair relay is probably better quality and by loosing the internal relay you will end up with less of a snake pit in the end cap. If you upgrade the power wiring, just make sure to get it all. The switch on the compressor is going to have smaller wire IIRC because it only controls the relay. Be prepared to find absolutely the lowest quality connections ever, with really poor soldering and take a good look at the thermal cut out. It's a wonder these things even run out of the box, heck back when they were all the rage many didn't.
While you are at it ditch the square metal motor cover. It just holds heat in.


Just for posterity this is the HF unit that started my insanity. The pressure switch was from a regular shop type compressor.

 

I'll resolder everything. I got ok at it messing with RC crawlers while I was back in school and didn't have any money or time for the real thing. As far as the thermal cutout are you just talking about cleaning up the connections?

 

Take another look at the pics of the brush holder. It was bent because the thermal switch (not in pic) was intentionally wedged between it and the end plate of the motor, almost looks like they were added as an after thought. Take a look at how yours is and make the call. I have no idea if it limits current and I don't remember if it was in the control loop or a power lead, I want to say it was in a power lead. Mine was discarded at the get go.

 

One more thing. Having the water separator/filter up close to the head will filter OK but the air going thru it could easily get to 400 degrees, not kidding. Any water will be vapor and pass on thru, condensing at some cooler point in it's travels.

 

Personally, in my opinion I would suggest against installing a pressure cutoff switch right at the compressor. The pulsation can cause premature cut-off of the compressor, Not that it would HURT anything, but it COULD cause the compressor to shut off before the storage tank actually gets to full pressure. I always mount my pressure switch on the tank itself.

 

Sound advice if there is a tank involved.
In my case, it's a portable unit with no tank and it functions consistently within a few lbs of spec. The pressure switch is just for "auto on/off". FWIW there is a plenum of sorts between the actual head and the finned "cover". Still alot of pulsation going on. I didn't want to locate the switch under the main line either, like a water trap, but heat seems to keep it dry.

For ARBs I would definitely recommend a tank, at least a small one.

 

The pulsation was my original concern with mounting the pressure switch on the compressor. Since I'm going to do all this work on the compressor in going to pull it out of the truck. I'm going to rotate it 180* in place and leave the head oriented in stock form when it goes back in the truck. I'm going to tap my stock air box and pick up a line to feed the compressor filter air. It's only about 6 inches from the box. I'll plug the original outlet hole and use the hole where the pressure switch is now to feed the system. I'll drill and tap it larger. This way I can move my air separator down the line. I'll mount the pressure switch after the separator vertically above the line to keep any mosture/derbies out of the switch. Lastly my rear bumper is a large steel 2x4 caped and sealed so that's my tank. After the T feeding the tank I'll add a regulator set at 90psi feeding the manifold for the ARB solenoids. So it should run: Compressor, line to separator, T for pressure switch, T feeding tank, regulator, manifold.

 

That should do it, the air line to the air box is a good thing, heck got to give the "Dick" credit now and then.
When you pull the head off to drill and tap, study the internals vs the intake/exhaust valve layout. There are two chambers inside the outer cover, one for intake, one for exhaust. Think twice drill once.

 

Sounds like a workable setup!

 

If you're planning on getting an ARB locker, you're going to have to plumb a line to the rear diff. And since you have to do that, you really have a lot of options of where to mount the pressure switch.

I decided to mount mine (along with ARB locker solenoid & pressure regulator) behind the back seat and away from the elements

 

I think I'm going to try putting the switch and solenoids in the cab. I think it will be healthier for them through the winters. I can't see the exhaust port on the solenoids but I assume you vented it to the outside through the floor. Am I Correct? Also I'm not going to drop another 7 bucks a piece on the ARB stab fitting for the exhaust as they aren't holding any pressure back for more than a split second. I'll use 1/8 NPT fittings with a little extra tape. Do you think the vinyl 1/8npt male to barb for a hose is strong enough or should I grab a brass fitting for the exhaust?