Now that I’ve made the pump as efficient as possible, it is time that I turn my attention to the valve. I am going to attempt to add volume in parts of the valve and take away volume in others. In this way, I’ll hopefully add power without adding to the number of pumps.
First, I’m going to modify the metal abutment washer. Here’s what it looks like stock:
Let’s go ahead and take a peek at the stock daisy 880 valve so these mods will make sense:
As you can tell from the above picture, the top part of the valve holds the greatest volume of air. Keeping this in mind, I ground down only the top of the metal abutment washer. In this way, I am maximizing the valve volume where it will most efficiently flow. Here’s what it looks like when complete:
I was careful not to remove too much from the pin area. Keep in mind that pin is the only thing holding the washer in place. If it fails while pumping, it’ll shoot forward – potentially hazardous to one’s health!
Next, I’m going to take a needle file and remove some material from the top of the valve body. I went ahead and removed the exhaust valve from the body. Here’s what it looks like prior to modification:
I took a needle file and coming from the abutment washer side of things filed the port nearest the valve seat. I filed it at a downward angle, improving the flow as well as adding a bit more volume:
For now, I’m going to leave the transfer port at the stock diameter and see where these mods have gotten me. Here’s another view of the modified valve from a different perspective:
I didn’t get a picture of the next thing I did, but it is easy to describe. Once the seal is placed on the abutment washer, I used waxed dental floss to build up the area between the seal and where I ground it down. In the future, I plan to 3d print a piece to take up this dead space.
I then put everything together and took her outside to chrony the results. Using 10.5 grain Crosman domes, I got an average of 661 fps with 10 pumps. I’m now producing 10.2 fpe with 10 pumps, and have as much energy at 25 yards as the stock Daisy 880 made at the muzzle!