On-board air system ideas and suggestions?

[Apparition]

I have both a Viair OBA and a portable system. The portable one has a built in pressure switch which would make your system way easier.

IMO I’d get a longer hose before I’d go to the hassle of making it removable. Or get a power tank.

 

[TJim]

I have both a Viair OBA and a portable system. The portable one has a built in pressure switch which would make your system way easier.

IMO I’d get a longer hose before I’d go to the hassle of making it removable. Or get a power tank.

I have a TMAX air compressor, with no pressure switch. I do not want to buy a new one right now so I am up to do the required mods on my own. I like learning and doing new stuff.

A longer hose would not really solve this problem, since I would like to use it both hard mounted in my TJ, mainly because of the space, but also to take it on trips with a different vehicle (portable).

 

[TurboTJ]

Why are you installing a pressure switch?

 

[TJim]

Because I would like to use a closed chuck air hose like this one : https://www.amazon.com/dp/B0036ULEV0/?tag=wranglerorg-20

I explain the reasons in this thread's post #17:
https://wranglertjforum.com/threads/what-tire-inflator-gauge-do-you-use.30894/post-499418

 

[dbbd1]

If you swap/reverse the hose couplers, so that the open-ended one is on the compressor, you won't need to worry about a pressure switch.

Just sayin'

 

[TJim]

If you swap/reverse the hose couplers, so that the open-ended one is on the compressor, you won't need to worry about a pressure switch.

Just sayin'

I did not quite get that.

 

[dbbd1]

Usually, the female coupler is on the air supply, the male is on the tool. Put the straight-through male on the air supply (compressor) and the female on the tool or tire chuck.

In other words, as long as the coupler is straight-through, not one that seals off, you won't have a problem.

 

[xxdabroxx]

If the compressor is allowed to build pressure on a closed off hose you need a switch to control it.

youll also need a check valve on the output of the compressor.

 

[Mr. Bills]

If you swap/reverse the hose couplers, so that the open-ended one is on the compressor, you won't need to worry about a pressure switch.

I did not quite get that.

Usually, the female coupler is on the air supply, the male is on the tool. Put the straight-through male on the air supply (compressor) and the female on the tool or tire chuck.

@TJim,

I think you are making the project far too complicated.

You don't need pressure switches, etc. if you plumb a simple system.

It is also unrealistic to think that you will be using your compressor as a portable unit once you go to the trouble of hard mounting it. Just buy a longer hose such as the Flexzilla 25' x 1/4" version, shown here with my Viair 400P portable unit:

Here is a simple onboard system that does everything one needs to fill tires, etc. (It does not store air for ARB air lockers or an air horn but it doesn't need to.) Note that the output fitting is a male swivel, not the usual female fitting, because the system is plumbed just like a portable system, i.e. with an open chuck.

Here is close up of the compressor head with brass fittings and a Viair check valve:

See this link:
https://wranglertjforum.com/threads/how-to-simple-onboard-air-for-your-tj-lj-viair-400h.10235/


My system uses a check valve at the compressor head even though it is an open system. Although unnecessary in an open flow system, one benefit of a check valve is there will never be pressure on the piston or valves on initial start up which will draw fewer amps than if starting under pressure. A check valve will also isolate things that need to be under pressure from things that do not and is better designed for that purpose that the piston rings and valve ports of a compressor. Check valves are less than $15 on Amazon.

If you simply must run a closed chuck on the end of your air hose, you could install a "tee" and inline pop-off valve to blow off pressure if it takes too long moving from tire to tire. 85-100 psi would be good pre-set pressures for that. However, my experiments with a Viair 400P compressor suggest that there is plenty of time to move from tire to tire with a closed chuck without blowing up a 25' hose (typically rated to 300 psi) or harming the compressor (maximum working pressure of Viair 400 series compressors is 150 psi), particularly if one uses a check valve at the compressor head.

Here, you can see a pop-off valve in a testing manifold I made from leftover brass parts:

As far as wiring is concerned, I used a Blue Sea P/N 5024 battery top fuse block, 10 ga. wire and a 40 amp fuse. Since my compressor is wired directly to the battery, the wire run is short and there is a built-in switch in the Viair 400H compressor, no relay is necessary for my system. You will want to use a relay or constant duty solenoid if you locate the switch inside the cab.

For an open flow system the wiring schematic in post #10 should work just fine.

I have used this wiring diagram for many years, originally published by Currie Enterprises in the 1990's when Currie was marketing 12v onboard air systems:

Notes:

An "unloader" performs the same function as a check valve but with the added feature of bleeding off pressure from the compressor cylinder head when the compressor stops pumping. A standard check valve is sufficient, such as the check valves marketed by Viair.

A pressure switch is unnecessary and serves no practical function unless you are using an air tank and need the compressor to turn "on" when tank pressure drops below a certain level and turn "off" when it reaches a certain higher level. A compressor pressure switch is not practical to set tire inflation pressures. Use an air gauge or specialized inflator tool for that.

A pop-off valve could be plumbed into the system at the manifold where the pressure gauge is shown. The pressure gauge is only useful in a closed system with air tank and would be omitted in an open system.

Finally, a constant duty solenoid and a relay perform the same function. Use what you have available locally, being sure that whether it be constant duty solenoid or relay that it has the appropriate amp rating for use with your compressor.




Best of luck with your system.

 

[xxdabroxx]

@TJim,

I think you are making the project far too complicated.

You don't need pressure switches, etc. if you plumb a simple system.

It is also unrealistic to think that you will be using your compressor as a portable unit once you go to the trouble of hard mounting it. Just buy a longer hose such as the Flexzilla 25' x 1/4" version, shown here with my Viair 400P portable unit:



Here is a simple onboard system that does everything one needs to fill tires, etc. (It does not store air for ARB air lockers or an air horn but it doesn't need to.) Note that the output fitting is a male swivel, not the usual female fitting, because the system is plumbed just like a portable system, i.e. with an open chuck.


Here is close up of the compressor head with brass fittings and a Viair check valve:


See this link:
https://wranglertjforum.com/threads/how-to-simple-onboard-air-for-your-tj-lj-viair-400h.10235/


My system uses a check valve at the compressor head even though it is an open system. Although unnecessary in an open flow system, one benefit of a check valve is there will never be pressure on the piston or valves on initial start up which will draw fewer amps than if starting under pressure. A check valve will also isolate things that need to be under pressure from things that do not and is better designed for that purpose that the piston rings and valve ports of a compressor. Check valves are less than $15 on Amazon.

If you simply must run a closed chuck on the end of your air hose, you could install a "tee" and inline pop-off valve to blow off pressure if it takes too long moving from tire to tire. 85-100 psi would be good pre-set pressures for that. However, my experiments with a Viair 400P compressor suggest that there is plenty of time to move from tire to tire with a closed chuck without blowing up a 25' hose (typically rated to 300 psi) or harming the compressor (maximum working pressure of Viair 400 series compressors is 150 psi), particularly if one uses a check valve at the compressor head.



Here, you can see a pop-off valve in a testing manifold I made from leftover brass parts:

View attachment 147950



As far as wiring is concerned, I used a Blue Sea P/N 5024 battery top fuse block, 10 ga. wire and a 40 amp fuse. Since my compressor is wired directly to the battery, the wire run is short and there is a built-in switch in the Viair 400H compressor, no relay is necessary for my system. You will want to use a relay or constant duty solenoid if you locate the switch inside the cab.

For an open flow system the wiring schematic in post #10 should work just fine.

I have used this wiring diagram for many years, originally published by Currie Enterprises in the 1990's when Currie was marketing 12v onboard air systems:

Notes:

An "unloader" performs the same function as a check valve but with the added feature of bleeding off pressure from the compressor cylinder head when the compressor stops pumping. A standard check valve is sufficient, such as the check valves marketed by Viair.

A pressure switch is unnecessary and serves no practical function unless you are using an air tank and need the compressor to turn "on" when tank pressure drops below a certain level and turn "off" when it reaches a certain higher level. A compressor pressure switch is not practical to set tire inflation pressures. Use an air gauge or specialized inflator tool for that.

A pop-off valve could be plumbed into the system at the manifold where the pressure gauge is shown. The pressure gauge is only useful in a closed system with air tank and would be omitted in an open system.
...

I disagree that a pressures switch is unnecessary and serves no practical function. For me it gives the compressor a break between tires without me going into the cab and turning the compressor off. Then its ready to go when I hook up to the next tire. That way if I'm not trying to nascar pitstop my re-inflation I can stop and have conversation without messing with my compressor. They don't cost much and are not difficult to install if you are permanently wiring your compressor. I think it's worth it.

I have the same hose and it's great, nice and flexible. I may trim a few feet off of mine after I use it a few more times. I'd like to air up another vehicle first to make sure I don't need the few extra feet. I need to get me a velcro strap like you have too.

 

[CharlesHS]

When I drove my '98 XJ 4.0L to Moab, Johnson Valley and similar events which required airing down I set up OBA in the Jeep; which consisted of a 3.5 gallon pancake tank in the factory spare tire location, a Viair 400H, a 50/90 psi pressure switch, a 3/8" copper line with several 6" circles (heat sink), and a 25' length of 1/2" air hose to fill up the tires.
I installed the pressure switch so the air tank always had pressure and would turn the compressor on automatically. The OBA also supplied air to the front ARB with a 2 way air flip switch.
This setup worked very well for over 15 years before selling the Jeep.

 

[LONGJP2]

After deciding not to hard mount mine... as the OP is trying to do.
I installed a 12v outlet in the rear of my jeep specifically for my compressor (Viair 450P). A heavy duty plug that could handle the amps, plus the appropriate wiring all the way to the battery. While I can use the outlet for other things, I have to keep in mind that I can't let somebody else plug my compressor into their normal 12v outlet. It is, however, set up with a quick disconnect plug so the alligator clips can be put back on.

 

[Mr. Bills]

I disagree that a pressures switch is unnecessary and serves no practical function. For me it gives the compressor a break between tires without me going into the cab and turning the compressor off. Then its ready to go when I hook up to the next tire. That way if I'm not trying to nascar pitstop my re-inflation I can stop and have conversation without messing with my compressor.

You are putting more stress and strain on your compressor by stopping and starting it between each tire than you would if you let it run - whether open or closed chuck.

It appears that you are using a closed chuck with a Flexzilla hose, which is rated to 300 psi. Your compressor probably has a maximum output of no more 100-150 psi. You are not going to blow up your hose by leaving your compressor running, so try this:

Leave your compressor running as you casually move from one tire to the next. Don't rush but don't purposely delay more than a bit. Count the seconds that pass and listen to the changes in the pitch of your compressor. Connect the hose to the next tire.

If you are using a typical 12v compressor rather than an Oasis or other high powered unit your compressor probably won't even be close to its maximum output when you connect the chuck to the next tire. I experimented with mine using the "test manifold" pictured above and learned that even when distracted and delayed while moving an air hose with closed chuck from one tire to the next that the pressure in the air hose never exceeded 85 psi, which was about the same pressure that my compressor began to sound like it was working harder.

I purposely timed how long to get to 100 psi. The purpose of this experiment was to demonstrate that my simple system was safe even if someone inadvertently used a conventional closed chuck rather than the intended open flow chuck and left the compressor running without the hose being connected to a tire. I can't find my notes right now, but I recall becoming impatient waiting. I specifically recall that the change in pitch of the compressor gave me plenty of advance warning that I should start thinking about moving the hose toward the next tire or that I should turn the compressor "off." I recall no need to rush.

My conclusion from that experiment was that a pop-off valve is always a good safety feature, but not absolutely necessary for my system. Another conclusion that could be drawn is that since the experimental evidence shows that starting and stopping a Viair 400 compressor between tires isn't necessary with a 25' 1/4" dia. Flexzilla hose and closed chuck, a pressure switch to start and stop the compressor is similarly unnecessary and adds needless complexity.

I respectfully submit that a pop-off valve preset for 50-75% of the maximum rated output of your compressor would be a simpler means for resolving any concerns you may have for overloading it should you become overly distracted while airing up your tires.

 

[TJim]

@Mr. Bills

I really appreciate all your advices and the time you dedicated to respond!

A lot of useful info, nice diagram. Especially the check valve, and the unloader valve.

The main reason that I "overcomplicate" and "overthink" my projects is because I am young and new to the 4x4/overland world, so I really enjoy learning new things and trying to explore all the possible ways to build something on my own. (within a reasonable budget)

Firstly, I do not really think that it is unrealistic to unmount the compressor when I hard wire it for two reasons:
a) I want to use it in a different vehicle as well (not when my TJ is there)
b) My TJ is my daily driver, and my Compressor a bit cheap (T-MAX air compressor), so I dont really want to carry it all the time under the hood (10kg), as well I dont really think that I should stress it in long periods of time that I will not use it (So I will mount it only during trips, etc.). The procedure to mount-unmount it should be quite easy ( 4 bolts, 2 wire connectors, and 1 air hose)

Secondly, I think that the pressure switch, is a quite easy and cheap mod that will allow me to not be in a rush, but also not to unnecessarily my air hose, or air compressor.

Lastly, I have almost decided the "final project", which might seem a bit overcomplicated or unnecessary, but I just like spending time with my uncle and building this stuff.

I am going to post the complete final idea in a few days, because I found all the suggestions and advices quite useful.

 

[Apparition]

You are putting more stress and strain on your compressor by stopping and starting it between each tire than you would if you let it run - whether open or closed chuck.

It appears that you are using a closed chuck with a Flexzilla hose, which is rated to 300 psi. Your compressor probably has a maximum output of no more 100-150 psi. You are not going to blow up your hose by leaving your compressor running, so try this:

Leave your compressor running as you casually move from one tire to the next. Don't rush but don't purposely delay more than a bit. Count the seconds that pass and listen to the changes in the pitch of your compressor. Connect the hose to the next tire.

If you are using a typical 12v compressor rather than an Oasis or other high powered unit your compressor probably won't even be close to its maximum output when you connect the chuck to the next tire. I experimented with mine using the "test manifold" pictured above and learned that even when distracted and delayed while moving an air hose with closed chuck from one tire to the next that the pressure in the air hose never exceeded 85 psi, which was about the same pressure that my compressor began to sound like it was working harder.

I purposely timed how long to get to 100 psi. The purpose of this experiment was to demonstrate that my simple system was safe even if someone inadvertently used a conventional closed chuck rather than the intended open flow chuck and left the compressor running without the hose being connected to a tire. I can't find my notes right now, but I recall becoming impatient waiting. I specifically recall that the change in pitch of the compressor gave me plenty of advance warning that I should start thinking about moving the hose toward the next tire or that I should turn the compressor "off." I recall no need to rush.

My conclusion from that experiment was that a pop-off valve is always a good safety feature, but not absolutely necessary for my system. Another conclusion that could be drawn is that since the experimental evidence shows that starting and stopping a Viair 400 compressor between tires isn't necessary with a 25' 1/4" dia. Flexzilla hose and closed chuck, a pressure switch to start and stop the compressor is similarly unnecessary and adds needless complexity.

I respectfully submit that a pop-off valve preset for 50-75% of the maximum rated output of your compressor would be a simpler means for resolving any concerns you may have for overloading it should you become overly distracted while airing up your tires.

My Viair 400p automatically shuts itself off. It was designed that way, internal pressure switch.

 

[pagrey]

You are putting more stress and strain on your compressor by stopping and starting it between each tire than you would if you let it run - whether open or closed chuck.

It appears that you are using a closed chuck with a Flexzilla hose, which is rated to 300 psi. Your compressor probably has a maximum output of no more 100-150 psi. You are not going to blow up your hose by leaving your compressor running, so try this:

Leave your compressor running as you casually move from one tire to the next. Don't rush but don't purposely delay more than a bit. Count the seconds that pass and listen to the changes in the pitch of your compressor. Connect the hose to the next tire.

Have you done this? Makes so little sense I can't really wrap my head around it. You are seriously recommending somebody repeatedly, intentionally ramps up their compressor to max pressure instead of installing a switch or simply shutting it off. Strange advice, I've never heard anything like this before.

 

[Jerry Bransford]

There is no need for or benefit to using a relay for that device. You can connect to the PSD's 12v input power lug to get power. Also there's no need for an unloader valve with an electric compressor like you're using.

Like shown here...

 

[xxdabroxx]

I don't get the inhibition of shutting off a compressor. Like you mentioned earlier the compressor rings are going to bleed down pressure similar to an unloader valve so you aren't really dead heading the motor. I feel like there is a benefit to letting the compressor cool down as I bullshit or enjoy a beverage than let it run it's ass off trying to make 150psi in a hose for no reason.

Mr. Bills

I really appreciate all your advices and the time you dedicated to respond!

A lot of useful info, nice diagram. Especially the check valve, and the unloader valve.

The main reason that I "overcomplicate" and "overthink" my projects is because I am young and new to the 4x4/overland world, so I really enjoy learning new things and trying to explore all the possible ways to build something on my own. (within a reasonable budget)

Firstly, I do not really think that it is unrealistic to unmount the compressor when I hard wire it for two reasons:
a) I want to use it in a different vehicle as well (not when my TJ is there)
b) My TJ is my daily driver, and my Compressor a bit cheap (T-MAX air compressor), so I dont really want to carry it all the time under the hood (10kg), as well I dont really think that I should stress it in long periods of time that I will not use it (So I will mount it only during trips, etc.). The procedure to mount-unmount it should be quite easy ( 4 bolts, 2 wire connectors, and 1 air hose)

Secondly, I think that the pressure switch, is a quite easy and cheap mod that will allow me to not be in a rush, but also not to unnecessarily my air hose, or air compressor.

Lastly, I have almost decided the "final project", which might seem a bit overcomplicated or unnecessary, but I just like spending time with my uncle and building this stuff.

I am going to post the complete final idea in a few days, because I found all the suggestions and advices quite useful.

The more shit you have to bolt on your rig to go offroading for an afternoon the less likely you'll be to do it. Being that it isn't a super expensive compressor I'd mount it permanently to your Jeep then get a second one if you want to haul around in your second vehicle.

The easier it is for you to hit the trails the more you'll be willing to do so. To me that means having my tool bag strapped down to a footman loop in the back of the jeep and my recovery gear at hand all the time. Now I've got my air compressor permanently mounted and an air hose sits behind the passenger seat (takes a lot less space than the portable compressor did). None of this impedes my daily driving duties (when I DD the Jeep) and I don't have to load anything extra if I'm going offroad. Means a Sunday drive into the forest at a moments notice is no problem at all and I'm as prepared as I'm going to be on any given moment (minus chains, I don't haul them around unless I'm headed to the snow).

There is no need for or benefit to using a relay for that device. You can connect to the PSD's 12v input power lug to get power.

Like shown here...

View attachment 147983

You wan't to run that big of a wire through the firewall to a 40amp switch then back through the firewall to the compressor? Or am I missing something? That's where the power to my compressor comes from, to an inline fuse, to the relay. Relay has small switched power wire from inside the cab.

 

[Mr. Bills]

My Viair 400p automatically shuts itself off. It was designed that way, internal pressure switch.

The Viair 400P-Automatic has the automatic shutoff, touted by RV'ers I know as a nice convenience feature.

When I purchased my Viair 400P for my Xterra (without the auto shutoff) I worried that I had made a mistake by not paying the $65 extra for the upgraded model with pressure switch.

My experiment with the Flexzilla hose allayed my fears because I had plenty of time to get the hose with closed chuck from one tire to the next without turning the compressor "off" and "on."

Since I use an open chuck with the Viair 400H hardmounted in my LJ it really doesn't matter because the compressor just runs at no load between tires.

 

[Jerry Bransford]

You wan't to run that big of a wire through the firewall to a 40amp switch then back through the firewall to the compressor? Or am I missing something? That's where the power to my compressor comes from, to an inline fuse, to the relay. Relay has small switched power wire from inside the cab.

Why is an additional switch in addition to the switch on the compressor needed? I run an even heavier gauge wire to the rear of my TJ for my trailer. The KISS principle is especially applicable to electrical devices.