Maintenance Modified assembly procedure for the regulator and air cylinder on original Evol models...


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Overview of the long post: On the original generation Evol's, to prevent the threads cutting the o-rings upon re-assembly, first install/push the regulator deep down into the air cylinder so the o-ring is just past the threads. Then screw on the air cylinder onto the receiver, ensuring the regulator is centered as it starts into the receiver's plenum. When the cylinder is fairly tight and the end cap is aligned with the chassis, fill it with a little air to push the regulator in place within the receiver/plenum to seal the system.

On the original Evol model's there is a chance of cutting the large o-ring on the regulator when putting the regulator into the receiver plenum and then screwing on the air cylinder. These thin cuts cause micro leaks and allow o-ring extrusion; both of which I had this week. Upon re-assembly I discovered that a modified installation process prevents this from happening. I disassembled and reassembled the Evol twice to ensure it worked well and to take these pictures.

Words of wisdom recently bestowed onto me about these micro leaks from this cut o-ring: If owner's would not feel the need to take these apart after they are sent out from the factory, then they would not leak...

But alas, I am a lifelong tinkerer and educator. Here's my assembly and installation procedure:

First, with acetone or alcohol, clean all the parts, threads, and surfaces of the old lube and debris. Then lightly lube the new o-rings and/or the regulator grooves and install them on the regulator. I use manufacturer recommended Krytox GPL-205 grease. Ultimox 226 grease is also recommended and used in the factory assembly procedure.

Second, on the clean receiver, lightly lube just the inside of the receiver plenum area where the smaller o-ring will slide into on the beveled edge. (Shown in the picture where the cotton swab sits.)

Third, lightly and carefully apply lube deep inside of the air cylinder on the sealing surface, just past where the threads end. I use my fingertip or a cotton swab and spin the cylinder to get it evenly around in there.

To prevent thread galling and seizure it is recommended by Tom to apply Krytox or Ultimox to the threads as an anti-seize. I've galled threads on other guns using pure silicone grease, and have never experienced galling after using Krytox. At no time should pure silicone grease be used on threads to prevent seize or galling.

Now for the assembly procedure:

Push the regulator strait down into the air cylinder untill the larger diameter o-ring is clear of all the threads and rests on the smooth freshly lubed cylinder. The regulator will be sitting so the small o-ring is just inside the end of the cylinder and the anodized portion slightly protrudes. If you push it in too far, pull it back out some until the big o-ring just contacts the threads. Also, the regulator is likely to sit a little bit sideways and will need to be centered in the cylinder bore for proper final alignment at assembly.

To begin assembly of the air cylinder, hold the receiver vertically and look down at the poppet valve to ensure that it is sitting on the valve. If it is not, lightly tap the side of the receiver with your palm and it should fall into place. Now, carefully thread the cylinder onto the receiver. It is important to ensure that the regulator is centered and starts spinning it's way into the lubed receiver plenum area. When the cylinder is fully threaded on and it's aligned with the receiver and chassis, it is time to fill it with air. The next steps will slowly fill it with air and seal the regulator in place.

Again with the gun kept in a vertical upright position, lightly tap the side of the receiver with your palm so as to align and settle the poppet valve down onto its seat. After this, lightly tap the butt stock down on the floor to ensure seating and slowly fill it with just a little air pressure. A couple of hundred pounds of air pressure will easily push the regulator into place against the receiver flange and seal everything. If air is escaping through the barrel port simply put your thumb over it and lightly tap the butt of the gun on the floor again and this should seat the poppet valve. A high air pressure blast may not seat the poppet as easily, and is harder to seal the escaping air with your thumb too, so I've found it's best to go slow and with back pressure on the port. If hand pumping, initially seal the barrel port with your thumb to seal the whole system and then pump away.
I hope this procedure helps you guys out.

Edited to remove unnecessary steps.


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Great post! I installed my regulators just as you did here and had no issues, cant say if the previous owners did or not as both rifles had clearly been opened up. Only reason I opened my new paradigm was to bring the speed back down a little bit. Not every rifle is the same and I do think that each can have their performance optimized by the end user if they know what they are doing. Different elevations, climate, etc can change each rifles behavior.
I will say when I do my reg I just put it in the reciever and then screw the airtube over it. Haven't had an issue this way. But can understand if others have
With regular shooting sessions I didn't have a perceived issue with the procedure of putting the regulator on the receiver and screwing on the cylinder. Upon leaving the gun sit idle for a month it had time for it to loose half it's normal fill pressure, to below regulator pressure. I've got a theory that when they are taken apart and put back together many times and the threads begin to get some galing from dirt and residual silicone lube on them, then the threads can get these micro sharp burrs on them which in turn cuts the o-ring just enough to cause a slow leak.
@mr007s Here's the assembly procedure that I do, so as to prevent slicing up those o-rings on the threads. One of these two types of assembly lube is important to move the regulator in place smoothly with a little air pressure. Do not use silicone grease on the threads.

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