Viair 400P Gauge Accuracy

[ArkRVHog]

So based on positive reviews from many forum users, I purchased this product and just tried it for the first time. I never saw any comment about a warning message they post on the hose next to their large air gauge which reads-

"Please Note: During inflation, due to air velocity, gauge pressure reading will be slightly higher than actual pressure. To gain accurate pressure reading, momentarily stop inflation by TURNING OFF the compressor, read pressure, then, if more pressure is needed, simply TURN ON compressor to continue inflation to desired pressure." (All caps my emphasis)

So to get an accurate reading on their fancy gauge, I've got to SIMPLY run around my RV multiple times turning off then back on the compressor? How ridiculous is that? I realize you could have a pocket gauge you use to accurately check it, but for a $225+ unit, I would expect more.

Plus, their gauge seemed to read about 3 PSI LESS and not MORE than the actual tire PSI when I checked it with another gauge...that's kind of backwards from their warning. Maybe I'm expecting too much but very disappointed to discover this limitation...anyone have a heavy duty (150PSI rating) compressor with an ACCURATE gauge on it?

[rsdata]

that warning would be the same for any air compressor...

the air gauge built-in is reading higher pressure air before being forced into the hose attached into your tire...

and you believe that your gauge is accurate?

WHy not just use the switch on the compressor? I have a cheaper model of the Vair and mine has an on/off switch, so why run around the truck to turn yours off?

I believe you protest too much...

[SailorSam20500]

On mine, the gauge is on the inflater. When I release the valve to stop air flowing into the tire, the gauge reads within +/- 1 lb of my slime gauge and the TPMS sensors. No need to run back to the compressor to turn it off.

[TitanMike]

Avoid the aggravation. Remove the gauge, plug the hole with a proper plug, and just use a tire pressure gauge.

Unless you want to install a compressor that has a storage tank, a pressure switch, and hose with inflator/gauge that's the way these compressors work.

You can't just install an inflator that you can add air, release handle, check pressure, and add more if necessary. These simple compressors will almost instantly stall when the pressure in the hose builds to it's limit and the "pressure switch" is the fuse. Your procedure would then be add air, release to check pressure, watch pressure climb to top of gauge. Compressor would then shut down and if you needed more air, a fuse would be needed. That could get real old, real quick.

One thing that will make these small compressors easier to use (unless filling a totally flat 22.5" tire) is to find a dual foot piece off a truck tire inflator. Remove the screw on connector on the end of the hose (if so equipped) and connect the "dual foot" piece, probably need a pipe coupler of the proper size.

This way you let the compressor run, air will continue to flow through the new "foot". Add air, remove the foot, check pressure with gauge, rinse/repeat as necessary. After a few "top off sessions" you get a feel of how long to leave the hose pressed on the valve stem.

BTW, the accuracy on these compressor gauges is equal to their price. Not very much. The gauges used probably cost less than a buck to the manufacturer of the compressor.

[LegacyFB38]

Originally Posted by ArkRVHog

...

So to get an accurate reading on their fancy gauge, I've got to SIMPLY run around my RV multiple times turning off then back on the compressor? How ridiculous is that? I realize you could have a pocket gauge you use to accurately check it, but for a $225+ unit, I would expect more.
…

You may be happier with an "automatic" compressor such as the 400P-RV and others.

From Viair website:

"Portable compressors with automatic shutoff come into play when moving from tire to tire, and when checking tire pressure in the middle of a tire fill. A typical portable compressor must be turned off between tire fills, and anytime you want to check tire pressure. If you aren’t near the compressor, this can turn into running laps back and forth to the portable compressor to turn the unit on and off. Automatic portables do not work in this fashion and will save you time & effort to get tires inflated quickly."

[CampinGpa]

Originally Posted by LegacyFB38

You may be happier with an "automatic" compressor such as the 400P-RV and others.

From Viair website:

"Portable compressors with automatic shutoff come into play when moving from tire to tire, and when checking tire pressure in the middle of a tire fill. A typical portable compressor must be turned off between tire fills, and anytime you want to check tire pressure. If you aren’t near the compressor, this can turn into running laps back and forth to the portable compressor to turn the unit on and off. Automatic portables do not work in this fashion and will save you time & effort to get tires inflated quickly."

That is way I got the Viair 450 Automatic. I hope it works .been too darn cold in Nebraska. Ordered it in January and got it in about 4 days cant wait to try it .

[ependydad]

I have the 450P and it’s gauge sucks. Anywhere from 5-10psi over.

I’ve got a new DIY inflator/gauge here in a box to test out.

[babock]

I use the gauge on the Viair as a guide. I use a real tire pressure gauge to accurately measure the pressure. The Viair is actually fairly close, what it reads while you are doing the inflating will never be correct and was never meant to be. I can see if you think that is the actual pressure that you would be disappointed.

[ArkRVHog]

Originally Posted by rsdata

that warning would be the same for any air compressor...

the air gauge built-in is reading higher pressure air before being forced into the hose attached into your tire...

and you believe that your gauge is accurate?

WHy not just use the switch on the compressor? I have a cheaper model of the Vair and mine has an on/off switch, so why run around the truck to turn yours off?

I believe you protest too much...

So based on your response and others, I'm fighting physics thinking the gauge should read accurately on this type of compressor...I get that now. But the actual compressor is located very close to the battery source not at the tire thus the many steps I see back and forth if you want to use the Viair gauge. Is yours different?

[ArkRVHog]

Ependydad...it sounds like any gauge won't work based on the way this compressor is engineered. If your new one does work (without shutting off the compressor to use it) I would love to know the model...thanks.

[ArkRVHog]

Originally Posted by LegacyFB38

You may be happier with an "automatic" compressor such as the 400P-RV and others.

From Viair website:

"Portable compressors with automatic shutoff come into play when moving from tire to tire, and when checking tire pressure in the middle of a tire fill. A typical portable compressor must be turned off between tire fills, and anytime you want to check tire pressure. If you aren’t near the compressor, this can turn into running laps back and forth to the portable compressor to turn the unit on and off. Automatic portables do not work in this fashion and will save you time & effort to get tires inflated quickly."

Actually I did buy the VIAIR 400P AUTOMATIC and this model specifically has the tag on the chuck hose (next to the gauge) about needing to turn the compressor off to get an accurate gauge reading. I was sure hoping it was just a matter of returning and replacing it with a different model. And the RV version just has an additional hose and some extra fittings I think...the actual compressor is the same. I'm going to call Viair tomorrow for some guidance...ugh.

[babock]

Originally Posted by ArkRVHog

So based on your response and others, I'm fighting physics thinking the gauge should read accurately on this type of compressor...I get that now. But the actual compressor is located very close to the battery source not at the tire thus the many steps I see back and forth if you want to use the Viair gauge. Is yours different?

My gauge is right at the inflator which is the way it should be. If you don't have one like that, just buy one. Should attach with a quick connect.

[CHICKDOE]

have the viair 400 and i do not have to go to the compressor to turn it off except when connecting the power leads to the battery. i have several analog and a couple of digital tire pressure gauges and they all vary. the two digital ones actually read the same. there is about a 3 psi difference between the viair gauge and the digital one that is my 'master'. so if i want 110 psi i inflate until the viair says 113 psi at rest and when i disconnect it and put my digital gauge on the tire i will be at 110 + or - perhaps .5 psi. and when i disconnect the viair i do not go to the compressor to turn it off.

[10Ranger]

I have the 400P-RV. It shuts down automatically when I release the handle. I just go from tire to tire without ever having to run back to the compressor. It came with two 25' hoses so I can reach all the way around the TV or RV. As for the gauge, I check it against my dial gauge and it is always spot on. It does read 4-5 pounds high while adding air but drops back to static pressure when the handle is released. Once you use it a few times you can usually stop it at the correct pressure.

[ependydad]

Originally Posted by ArkRVHog

Ependydad...it sounds like any gauge won't work based on the way this compressor is engineered. If your new one does work (without shutting off the compressor to use it) I would love to know the model...thanks.

For now (and the last 7 years I’ve RV’d), I just keep a digital gauge with me. I fill a bit, check pressure with the separate gauge, and then adjust as needed. I wouldn’t be running back to the truck each time just to get the Viair gauge to work right.

When I swapped emails with Viair about it, their recommendation was to let the gauge settle for a bit and then it would be accurate. Never worked out that way for me.

We’ll see if the new gauge works any better. I’ll actually top up all 12-13 tires tomorrow in prep for a travel day on Tuesday. I’ll give the new one a shot.

[Adrian Gordon]

Originally Posted by 10Ranger

I have the 400P-RV. It shuts down automatically when I release the handle. I just go from tire to tire without ever having to run back to the compressor. It came with two 25' hoses so I can reach all the way around the TV or RV. As for the gauge, I check it against my dial gauge and it is always spot on. It does read 4-5 pounds high while adding air but drops back to static pressure when the handle is released. Once you use it a few times you can usually stop it at the correct pressure.

Same here. Take my finger off the trigger for a minute and the compressor stops and the guage on the compressor handle drops down a few pounds to the actual tire pressure. It's always within a pound of what my separate guage and my TPMS show. Never have to run back to the compressor until I'm done and ready to put it away.

[Adrian Gordon]

Take it back and get the 400P-RV.

[ArkRVHog]

*****UPDATE*****
So I just got off the phone with a Viair tech support guy who confirms on the Model 400P Automatic, the needle gauge is plus/minus 3 PSI...but no need to turn unit off/on to get this inaccurate reading...really?!

Understanding my disappointment with this confirmation, he then shares they make a DIGITAL hose/gauge unit that is good to plus/minus 1 PSI...I can deal with that. ($39 on Amazon...item #00042 Digital Tire Inflation Gun, he said.)

If the needle gauge was at least CONSISTENT in being X PSI more or less, I could compensate for that but no such luck. I'm just surprised that the many Viair users on this forum haven't called BS on this in any previous threads I could find...go figure.

[ArkRVHog]

No difference in the unit/gauge except for the second coiled hose and some adapters I am told. Wouldn't solve this issue.