Why use a priority valve on your air filter?

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Brian10956

Brian10956

Member
Mar 15, 2017
1,804
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New York, United States
i have the alpha filter on my Carette compressor. It has a priority valve on it which makes sure the air going through the filter material is at 2000psi. For those of you who are giving the gold Chinese ebay filter a shot you may want to add on this accessory I cut this info from eBay.High Pressure Air Priority ValveOK ... you got yourself a new or not so new scuba diving or paintball compressor here on eBay or from the local dive shop. But you find that the filters cost an arm and a leg! Even the cheaper paintball filters are still expensive. What do you do? Install a back pressure regulator (Priority Valve) on the outlet of your filter. This will raise the pressure of the air in the filter housings to around 1800 PSI (pressure is user adjustable 300-5000 psi) before allowing it to flow out to the hose. What that does is to increase the density of the air, making the mechanical filter MUCH more efficient so the chemical filters don't have to work as hard. In fact, you can get an increase in efficiency of as much as 450%! This little gem will pay for itself in the first couple of filter changes!Installation is simple. Just remove the hose from the filter outlet. Install the valve between the filter and the hose. The priority valve has a 1/4" pipe female entry and two 1/4" pipe female outlets so you may need to get the appropriate fittings for your system.
 
I found this one at filtertechs.com.VL-530110-AF Priority ValveEconomy / Fits: 46150
Material: Aluminum / Gold Anodized
Max Rating: 6000 psi
Flow Rating: Max 50 SCFM
Size: 1/4" NPT-Female Inlet (2 outlet ports)
VL-530110-AFA priority valve is used on the outlet of a high pressure filter tower. The purpose of this valve is to maintain a certain pressure level inside the tower at all times regardless of what the downstream fill pressure might be. Also known as a "Pressure Maintaining Valve" the VL-530110-AF is factory set at about 2000 psi but can be adjusted if necessary. By maintaining a constant pressure of at least 2000 psi, the efficiency of the filter media inside the tower is increased as much as 400%. Having a properly set and functioning priority valve is critical to effectiveness of any high pressure purification system.Old Price: $95.71Price: $91.00You save: $4.71
 
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Brian10956, please post link for eBay High Pressure Air Priority Valve, I can’t seem to find it. Thanks. Also, how would this be much different than manually keeping your fill tank valve shut until compressor pressure is within a few hundred psi of tank pressure and then opening tank valve? I’d think that most of the time we aren’t filling from zero and are instead topping off from about 3000 to 4500 psi. 
 
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"Centercut"Brian10956, please post link for eBay High Pressure Air Priority Valve, I can’t seem to find it. Thanks. Also, how would this be much different than manually keeping your fill tank valve shut until compressor pressure is within a few hundred psi of tank pressure and then opening tank valve? I’d think that most of the time we aren’t filling from zero and are instead topping off from about 3000 to 4500 psi.
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The way this works it’s like a check valve on your filter cylinder your filter cylinder will fill to 2000psi before the air goes to your tank. That what your filter is filtering the air at a high pressure for all the air going to your tank. If you connect your tank to your filter and don’t open the valve on the tank until the pressure in the line is the same as what you started with it to my thinking will have the same effect. I just checked you way the air going through the filter will vary in pressure with the priority valve it stays at a steady 2000psi your way it will go up to 4500 psi which means the air goes through the filter eliments too fast therefore less effective. 
You can look at airtanksforsale web site to see what they say is the reason to have a PMV on your filter 

here is the eBay link but with shipping I think filtertechs.com is a little less

https://www.ebay.com/itm/SCUBA-or-Paintball-Compressor-Priority-Valve-PMV-Adjustable-NEW/152765190736?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D1%26asc%3D20160908110712%26meid%3D254eb31437164d70a076c929c18caf28%26pid%3D100677%26rk%3D2%26rkt%3D9%26sd%3D162748232449&_trksid=p2385738.c100677.m4598
 
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Brian, actually, the priority valve does what you describe initially, but once it gets to 2000 psi, or whatever the setpoint is, the pressure then goes up past 2000 psi to whatever you are charging your tank to. Once you are past the setpoint on the way up, the system pressure is the same on both sides of the priority valve. This is why the priority valve is important when filling tanks from zero, but not so much when topping off. 
 
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"Centercut"Brian, actually, the priority valve does what you describe initially, but once it gets to 2000 psi, or whatever the setpoint is, the pressure then goes up past 2000 psi to whatever you are charging your tank to. Once you are past the setpoint on the way up, the system pressure is the same on both sides of the priority valve. This is why the priority valve is important when filling tanks from zero, but not so much when topping off.
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I need to double check I thought that the priority valve also acts as a check valve only allowing air pressure over its calibration to exit but not allowing air from tank to return to the filter, again I’m not sure if once the valve hits 2000 the check valve is bypassed as you suggest. I will see if I can find out and report back
 
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"spysir"Brian, your likely right.
I think the point CC was making is, with the value - air will be pressurized to AT LEAST 2,000psi so the filter works best.
Most refill there tanks well ABOVE 2,000psi ( I refill my 4,500tank at 3,000psi) therefore the filter is already doing what it would with the extra valve.

john
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Yep. That's what JoeB. told me. The filter-media needs what he called "dwell" to work best. The pmv makes sure there's around 2000psi before opening. That way the air doesn't just flow straight thru without the media having a chance to do its job. I agree its probably needed more if you're filling a gun directly as the gun's pressure would be lower than a partially filled scba bottle.
 
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Exactly... It does act as a "back pressure regulator" to make sure that there is at least the set pressure (2000 psi in this case) so that until there is 2000 psi nothing passes the valve. So it will hold 2000 psi in the filter housing until the downstream pressure gets to 2000 psi. After that, the pressure will gradually build up on both sides of the valve until you reach the final pressure. So at 3000 psi, there will be 3000 in the filter and 3000 in the hose to the tank and 3000 in the tank. Same story at 4500 psi. What you don't want to happen initially is the air going through the filter to go too fast when the pressure downstream of the APV is low, less than 2000 psi. So until the pressure in the hose and tank are at least 2000 psi, it regulates pressure in the filter until the hose/tank are at or above 2000 psi. This is most beneficial to dive shops that almost always fill the dive tanks from very low pressure after divers bring them in to be re-filled. So when you top off a SCBA tank for PCP air guns, you are usually starting at much higher than empty, usually over 2000 psi. So the APV really doesn't get a chance to function as a back pressure regulator. In my younger days, I worked as a nuclear engineer for the Navy, so I'm pretty familiar with piping systems and high pressures... 
;)
 
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So now based on what has been said I guess we can conclude that if you are only filling tanks that have at least 2000 psi in them the priority valve is not needed. The whole purpose of the valve is so that Air passing through your filter media is at 2000 psi which allows the media to perform at its best. But users should not open their tak valve until the pressure has equalized.

Centercut when did you work for the Navy. I was at the nuclear power training school in New London in the late 60s. I specialized in maintaining the submarine internal navigation systems for the fleet out of Charleston SC aboard a Sub Tender. They wanted to send me to school for a masters degree in EE but I didn’t want to commit to another 6 year enlistment. 
 
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I added a male foster with a built in check valve on the input side of my Gold Filter and detailed the fittings used with photos in an LC-110 thread several months ago. Whenever I top off my 6.8L tank I open the tank valve first which pressurizes the filter to the pressure in the tank which is at least 3,000 psi. Output from the compressor cannot open the check valve until the compressor pressure exceeds the pressure from the tank. It is an economy priority valve replacement and serves 99% of the function as a PMV.

That check valve serves three functions. The first is not having to monitor the pressure building in the compressor to equalize to the tank pressure before opening the tank valve. That protects the compressor from being stalled by starting under load. The second is to increase the dwell time for any residual moisture to be captured by the filter after the moisture tower has already dumped most of it. As has been mentioned earlier in ths thread, the only time a Priority Valve provides any protection that the check valve doesn't is when filling a tank from empty. In most cases PCP tank owners are topping off tanks, not filling from empty like a fireman's tank or dive tank. The third function is to save any air that gets past the check valve from being lost should a leak occur in the compressor at any point before the check valve. A Foster check valve costs $3 from Aliexpress, vs. $91 for a Priority Valve which is rarely needed by an airgun tank owner.
 
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I use two check valves in my output line. One at the tank to prevent air loss in the event of something failing downstream with the extra benefit of auto equalizing as described by Humdinger above. I also use one at the compressor outlet which allows me to purge without losing any air. It also allows me to stop filling at any time and restart without having to relieve the pressure in the line and filter before restarting the pump
1566098866_5592679455d58c5b2551e93.98265062_20181212_140850.jpg
 These all have nonreturn plugs in the male foster QDs. As Humdinger stated, 2-3 bucks each. The DIN 300 tank valve adapter was about $15 USD.
 
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A priority valve has nothing to do with dwell time. That is determined by the size of the filter tower and the compressor flow rate. The PMV increases density of the air passing through the system. That makes the separator work WAY more efficiently and the zeolites in the filter work a lot more efficiently.



Ray Contreras - Owner - CompressorStuff.com
 
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