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Superflow MV90/Smittybilt 2781 Modifications

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Old 11-24-2013, 06:40 PM   #1
Nuggety
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Superflow MV90/Smittybilt 2781 Modifications

Many of us have purchased a Superflow MV90 or Smittybilt 2781 compressor for trail, safety or towing use. While it is a good value for the money, there's definitely room for improvement.

I'm going to keep a list of DIY modifications that can be done to these compressor to increase their quality. Please contribute and I will add a link below!

List of mods
Pressure switch
Improved air chuck



For reference, here is the un-modified unit:



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Old 11-24-2013, 06:40 PM   #2
Nuggety
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Pressure switch mod (Under $50)


Intro
One of the things that gripes me about this unit is that it is continuously blowing. If you need to replace the stock air hose, you are most likely going to get an off-the-shelf tire chuck that only blows when you depress a handle or if it's mounted to the tire. If the unit is on and you don't have things all hooked up, pressure builds up until it reaches a critical level and escapes out of the path of least resistance. This should be the blow-off valve, but for me, it was the cheap hose




On all of the home compressors you will ever see, this situation doesn't occur because they have what is known as a pressure switch, which is a mandatory safety item. This device will sense when the pressure in the compressor tank is too low, and will kick on the motor. Once a preset pressure is reached, the switch senses this and automatically shuts off the motor.

My goal is to add such a switch. Since our compressors are tankless, the pressure is held in the steel hose that doubles as the carry handle. When you attach a hose, that acts as a portion of the 'tank'.

From the pressure switches I've researched, they have a turn off pressure of 200 PSI or less, while hoses are rated between 100 PSI - 400 PSI. Based on the numbers, as long as I'm not buying the cheap hose, the pressures are well within acceptable ranges.

HOWEVER, AS ALWAYS, I am not responsible for any modifications you perform.


Parts needed
Some of these parts can be hard to track down since most compressor shops only deal with customers who have 1000 PSI units or bigger As a result, here's a result of off-the-shelf and easy to buy parts.

These parts are from Home Depot:
These parts you will need to find online (at least I can't find them local):
  • VIAIR 90223 90 / 120 PSI (30A) sealed pressure switch. My best price was from Summit Racing
  • VIAIR 92812 1/4" NPT male to 1/8" NPT female reducer. I again purchased from Summit Racing. WARNING! Do not buy a BSP to NPT reducer! the threads are not compatible!!

Note that you can buy unsealed pressure switches as well, which cost about half. However, I live in a wet climate and prefer not to get zapped
You can buy from other companies than VIAIR parts, but I couldn't find anything easily.

Misc. parts needed
  • Wire
  • Wire sleeving
  • zip ties
  • heat shrink
  • female spade connectors and butt connectors, OR solder.... whatever your desired method of connecting wires together is

Tools needed
  • Basic socket and wrench set. Maybe a monkey wrench, these nuts are crappy
  • Allen wrench set. I think I used a 5/8"
  • Wire strippers
  • Crimping tool
  • Soldering iron (at minimum, this will be used to de-solder some connections)
  • Multimeter
  • something to melt heat shrink

Stuff needed for testing
  • Car battery
  • Compressor hose that is compatible with the compressor, minimum pressure rating of 200 PSI
  • simple cheap air blow gun


Process
  1. Unplug the compressor (duh!)
  2. Unscrew the blow-off valve. If there's any gritty stuff on the threads of either the compressor or the valve, clean it up. You might have to get a knife and scrape it off a bit.
  3. Put plumber's tape on the threads of the following items:
    • Blow-off valve
    • tee
    • both ends of the male-male coupler
  4. Attach the blow-off valve to one of the female ends of the tee
  5. Attach the female-female coupler to the male end of the tee
  6. Attach the male-male coupler to the other end of the female-female coupler
  7. Take the entire assembly and screw it into the compressor



Apply plumber's tape to the reducer
Attach the reducer to the pressure switch
Attach the other end of the reducer to the tee


  • Remove the black base plate from the bottom of the compressor
  • Remove the front L bracket that is held on with the Allen bolts
  • Remove the NPT fitting and washer from the compressor's handle. Clean off any plumber's tape
  • Remove the heat shield by removing the Allen bolts
  • At this time, you can pull back the plastic cup that is holding the electronics
  • Making sure the switch is in the OFF position, connect the compressor to the car battery
  • Turn the multimeter to voltage DC
  • Take the black lead of the multimeter and ground it on the exposed, unpainted metal of the compressor
  • Take the red lead of the multimeter and test each prong of the power switch to determine which is the incoming hot lead (reads a voltage) and which is the outgoing lead (reads zero). For me, the outgoing was in the middle of the switch as shown below.
  • De-solder the incoming lead from the switch. YOU WILL NEED TO ATTACH TO THIS WIRE LATER ON, DON'T CUT IT OFF OR ANYTHING DUMB LIKE THAT! Clean up the prong as well by removing the excess solder.



We need to send some wires from the factory on/off switch to the new pressure switch.
Cut a hole in the plastic cup for the wire leads to exit. If you look on the bottom of the cup, there's some pre-made tiny holes. I used the opportunity to make them bigger. Bonus points since these are on the bottom of the cup, which hides the entry for aethetics and minor water resistance




Now, it is time to wire the pressure switch. The idea is to make it inline so that it will trip the system when pressure is reached


  • Using your spade connectors and butt connectors (or solder), your wire, and your heat shrink:
    • connect one end to the outgoing lead of the factory switch
    • connect the other end to the pressure switch (doesn't matter which wire)
    • connect the remaining end of the pressure switch to the wire that you de-soldered from the earlier steps.
    TIP: Keep enough length of wire to make any repairs easy to perform. You can shove some excess inside the cup.
  • Re-assemble the cup, metal plates, all that good stuff. Make sure to put some plumber's tape on the NPT fitting before attaching it. Don't overtighten anything, it doesn't need much.
  • Put on the wire sleeving and zip tie it up purty



I just realized I should have probably rotated my sleeving so the opening is pointing down, oh well...



Testing

This part can feel kind of sketchy, so I tried doing the best I could to protect against accidental explosions or mayhem, but still I'm wishing I had a better way to test. Anyway, here's what I did, trying to minimize any potential damage from problems:
  • Drive your vehicle into the garage
  • Open the garage door enough for vehicle exhaust to escape (if your vehicle is on)
  • Put compressor on ground next to driver tire. Put a wood board between the vehicle and the compressor in case anything happens
  • Attach the compressor hose (rated at 200 PSI or above) to the compressor
  • Attach the air blower to the hose
  • Holding the button down on the air blower, turn on the compressor. The compressor should kick on and your blower should start blowing. This is how your compressor normally operated before modding
  • Continue to hold down the air blower and walk into the house or behind a sturdy wall
  • Throw the air blower/hose around the corner and shut the door (if you have one).
  • Proceed to panic as you realize you've just trusted the internet and imagine how you've potentially created a bomb that will destroy your vehicle and kill someone, oh God what was I thinking, why didn't I just spend the extra $400+ and buy a compressor with a pressure switch from the factory that's been tested by professionals, oh God I'm an idiot...
  • Realize that the compressor has shut itself off and the pressure switch has done exactly what it needs to do (note the compressor will cycle occasionally if there are any air leaks). Also realize the blow-off valve acts as a protection device for overpressure
  • Congratulate yourself on what a huge success this was and how the internet is a magical place once again, oh, I'm sorry I ever doubted!!

(FYI, if you have a better test setup, I'll erase this suggestion and put yours in here )

More to come later... test video!
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Old 11-24-2013, 07:57 PM   #3
Nuggety
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Name: Mike
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Improved air chuck (about $25)

Unmodified compressors
The MV90/2781 compressors are unique in that their built-in chuck is constantly blowing. I haven't found an aftermarket replacement that is set up like that.
The best option is the VIAIR 00025 hose (purchase from Amazon here).
The benefit is that the guage is more accurate (typically within +/- 5 PSI from my experience), and it has a built-in deflation option.

WARNING! If you use this with an unmodified compressor, you must follow these steps when airing up tires:
  1. Attach hose to tire
  2. Turn on compressor
  3. Monitor pressure. When tire has reached desired pressure, turn off compressor
  4. Repeat for the other tires.
If you detach the hose from the tire without turning off the compressor, you will either rupture the hose or trigger the bleed-off valve.



Modified compressors

If you have done the pressure switch mod, you can use whatever you like. However, I highly recommend the ARB inflator chuck:
  • the tire gauge is very accurate
  • the chuck has a bleed-off button to reduce pressure. Doubles as a deflator!
  • the unit can be used without being hooked up to a compressor, so you can use it as a gauge/deflator by itself

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Old 11-24-2013, 08:20 PM   #4
Bad Spuller
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Nice job man. I may have to do this in the near future. I can tell that the super flow hose and chuck are not of the highest quality.. upgrade definitely needed.
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Old 12-02-2013, 12:57 PM   #5
Nuggety
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Name: Mike
Joined: Apr 2008, #5877
Location: Olympia, WA
Age: 34
Gender: Male
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Pressure switch mod section updated
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Old 12-06-2013, 03:51 PM   #6
          
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I copied your posts. Much Love'
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