Author Topic: HFT 500 air leak (Read 735 times - 1 votes)
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Iowa airguner · « **Reply #20 on:** November 13, 2024, 09:56:52 AM »

Well it held air all night.
The only thing that is different is all new O rings in the regulator and I cleaned everything.
The tension on the spring that holds the piston on the seat probably has more tension on it than it did originally. When I started to remove the brass spring holder it unthreaded after only two or three turns. And it is a little tighter now.

I ordered all the seals for the gun and a new piston but I think I’m gonna reassemble the gun and chronograph it before I mount the scope and stock.

I am actually really glad this all happened. Now I know the gun inside and out. That gives me confidence for some reason.

Iowa airguner · « **Reply #21 on:** November 13, 2024, 11:38:03 PM »

I fired it over the chronograph and it was shooting at 750 fps. Before all this started it was shooting 880 fps.

I had to increase the spring pressure on the firing valve to get it to seal. Would this increase in spring pressure cause it to shoot slower?

Looking at he seal and the block I wonder if they are just worn out.

Iowa airguner · « **Reply #22 on:** November 14, 2024, 06:05:21 PM »

After talking to some air arms people and showing them the photos they agree the valve and body are worn out. And increasing the spring pressure directly affects the power. So to get the seal with out excessive pressure I need to replace the parts.
Plus when I replace the valve block I will need to drill out the transfer port to match what I have now.
And the striker rod is getting replaced because I am not sure I can get the old one out without damaging it.

It’s another sixty bucks but now all the seals in the regulator and the gun will be new.

And I have GOT to get a compressor.
Hand pumping from zero after each adjustment was more than I need to do.

Iowa airguner · « **Reply #23 on:** November 14, 2024, 09:50:24 PM »

I have new parts coming so I decided to try using some polishing compound and lap in the valve. This actually worked and I got the gun to seal up with much les spring pressure on the valve. Yesterday it took 6 turns to seal and was shooting at 750 fps. Today after lapping the valve and 3.5 turns in I’m at 825 with 10.3 and 890 with 8.4 gr pellets. It was shooting 880 with the 10.3.

But I am going to leak test it until the parts come in.

Because after spending a week pumping up the gun with a hand pump. It failed.

Not sure what’s wrong. It pumps up to 1000 psi then gets real sticky and I cant pull up on it.

Took it all apart and everything looks fine. Won’t pump up my other guns either. I’ll order a compressor tomorrow.

Motorhead · « **Reply #24 on:** November 15, 2024, 12:05:14 AM »

A change in regulator set pressure ALSO has a direct effect on speed.
So as stated in post #15 ... unless reg is exactly the same pressure as previous, speed won't be either

Iowa airguner · « **Reply #25 on:** November 15, 2024, 03:43:20 AM »

The regulator pressure is a little bit higher than before.
Before resealing the regulator it was just above the 100 bar mark. Now it is between 100 and 150. The next time I have it apart I am going to move the regulator screw one notch in.

The high pressure O ring in my hand pump failed. So I ordered a repair kit and a compressor.

Motorhead · « **Reply #26 on:** November 15, 2024, 04:06:42 PM »

Quote from: Iowa airguner on November 15, 2024, 03:43:20 AM

The regulator pressure is a little bit higher than before.
Before resealing the regulator it was just above the 100 bar mark. Now it is between 100 and 150. The next time I have it apart I am going to move the regulator screw one notch in.

The high pressure O ring in my hand pump failed. So I ordered a repair kit and a compressor.

Now shooting slower ... case of slight valve lock

JPSAXNC · « **Reply #27 on:** November 15, 2024, 05:28:37 PM »

I don't know anything about your gun, but the poppet seal looks like black Delrin (acetate) which is way to soft for a PCP. White Delrin is harder, but PEEK is best. HTH

Iowa airguner · « **Reply #28 on:** November 15, 2024, 05:41:48 PM »

It’s not valve lock but an interesting balance.
I am very happy this all happened so I understand or think I understand what is happening. Forget the leak. That is the firing valve and seat. I’ll put in new ones and I have sealed the old one with some polishing compound.
But getting it back to the original shooting spec is my new task.
So
The two springs are working against each other with the valve in between.
If I increase the pressure on the valve. And the striker spring is the same. The striker hits the valve against a stronger spring and less air is released. As I reduce pressure more air is released so I get more power.
But I have to take the pressure in the air tube into account.
Before I was moving 10.3 grain pellets at
880 fps and the regulator was at 110 bar.
Now I’m moving 10.3 grain pellets at 835 fps.and the regulator is set to 130 bar.
So to increase the pellet speed I need less spring pressure on the valve seat . And I need to reduce the regulated pressure back to 110 bar so the striker spring will be pushing the valve open against less pressure.
Do I have that correct?

JPSAXNC · « **Reply #29 on:** November 17, 2024, 03:26:42 PM »

Just set everything back the way it was and put in a new valve poppet. The old poppet was beaten flat ( more surface area) so the original hammer strike could not open the valve as far.

Motorhead · « **Reply #30 on:** November 17, 2024, 03:42:33 PM »

Quote from: Iowa airguner on November 15, 2024, 05:41:48 PM

It’s not valve lock but an interesting balance.
I am very happy this all happened so I understand or think I understand what is happening. Forget the leak. That is the firing valve and seat. I’ll put in new ones and I have sealed the old one with some polishing compound.
But getting it back to the original shooting spec is my new task.
So
The two springs are working against each other with the valve in between.
If I increase the pressure on the valve. And the striker spring is the same. The striker hits the valve against a stronger spring and less air is released. As I reduce pressure more air is released so I get more power.
But I have to take the pressure in the air tube into account.
Before I was moving 10.3 grain pellets at
880 fps and the regulator was at 110 bar.
Now I’m moving 10.3 grain pellets at 835 fps.and the regulator is set to 130 bar.
So to increase the pellet speed I need less spring pressure on the valve seat . And I need to reduce the regulated pressure back to 110 bar so the striker spring will be pushing the valve open against less pressure.
Do I have that correct?

Not really.
For any given hammer spring energy exerted to the poppet, the resistance of a stiffer poppet spring is VERY minimal relative to force High Pressure is exerting holding the poppet closed.
If the original tune was set up correctly the plenum pressure and hammer strike were in near balance or In balance.
Now with a HIGHER plenum pressure the energy exerted by hammer & spring which a fixed value NO LONGER can sufficiently lift the poppet to yield a higher power shot and this is what VALVE LOCK IS

For if at this higher reg setting you had a STRONGER hammer strike on poppet you would utilize the pressure present in plenum and make more power !!!

Your running off the bell curve to valve lock side as currently set up ..... Truth

Iowa airguner · « **Reply #31 on:** November 17, 2024, 09:36:25 PM »

Thank you, I thought valve lock was when the pressure was so high the valve can’t open at all. I’m only up about 20 or 30 bar. So I’m guessing the valves is just feeling hight resistance than it would at 100 bar.

So rather than fool with the springs for now since I still have not received the new valve and body.
But just for testing I need to drop the regulator pressure back to 100 bar and then shoot it again with the same spring set up but lower bottle pressure. That should bring the FPS up because the valve can open further into the lower pressure.

My compressor and pump repair kit will be here Tuesday.

Here is the regulator settings chart that came with the gun. I did not intentionally turn up the regulator. I took it apart and replaced all the seals. But after reassembly it is now reading 130 bar on the gauge. Originally it was reading 100 bar or just above that.

One other thing there are two home made steel shims under the hammer spring to increase the striker force. I have not measured them but they are 2-2.5mm thick each.

Iowa airguner · « **Reply #32 on:** November 19, 2024, 05:43:04 PM »

The new valve seat has arrived and I am feeling pretty good about the repair. Even though it’s working now. You can see how worn the valve is compared to the new one.

Iowa airguner · « **Reply #33 on:** November 19, 2024, 09:08:52 PM »

I repaired my Hill pump and I got a compressor so I never have to use it again.

I have not gotten all the new parts yet but I wanted to mess with the regulator.
Total height is 60.09mm and the pressure was 150 bar and the tank was at 190 bar.

I fired a couple shots with 10.3 Diablo and the went 770 fps.

I changed the regulator height one turn. I had marked it but was one turn off when I pu it back together.
Now it reads just over 100 bar and the tank is over 190 bar. It is shooting 10.3 diablos are at 837fps. And truthfully it is shooting four and five duplicates in a row. I can live with it.
But I wanted to see if I reduced spring pressure on the seat would it up the speed of the pellet. It did not.
One half turn out and it would not seal. 1/4 turn out and it would seal half cocked then it filled up. I fired a bunch over the chronograph again and it’s still 835fps +~- 2.
I am going to get the rest of the parts tomorrow and rebuild the whole gun with new seals.
I already have the seal kit and firing valve.

Iowa airguner · « **Reply #34 on:** November 21, 2024, 11:30:56 AM »

Now I am in business. I got the new guide rod and valve block and it all looks correct.

The new valve seat is very smooth and has a slight taper. The old seat was definitely beaten flat. And has a definite groove.

Now I just need to drill the transfer port and polish all the internal parts to a mirror finish.

Let’s see if the power goes up from 835 fps. The old poser was 880fps. Anything consistent around 850 is good enough.

Iowa airguner · « **Reply #35 on:** November 21, 2024, 04:20:19 PM »

I put in the new parts. Everything looks good and it leaks worse than ever. Does not even try to seal even with extra spring pressure. I guess the seal needs to be lapped in or something.

Does anyone know a link to instructions on seating a firing valve? Everything I have found is about broken parts or modifications. Just trying to get the new parts to work. I put the old parts back in and they seal up just fine.

Iowa airguner · « **Reply #36 on:** November 21, 2024, 10:02:26 PM »

This is where I’m at. I put in the new parts. I used a little mothers to polish in the new valve and seat and got them to seal. I installed the new valve and the valve body. I drilled the transfer port out very carefully.
And after I couple tries I finally got it to seal with four turn in on the valve spring and it shoots at 720 fps. Thats way to slow.

So I pulled the new valve and dropped in the old valve that I cleaned up. And it sealed at 3.5 turns in the new valve seat. That what it was when I got it.

It finally sealed up with the compressor and was not leaking. So I shot 25 shots at 850 fps. And that’s close enough for me. I think my new valve stem might be a 12’ft lb valve. So I now have the new body old valve and as long as it is holding air I’m good with it.

HFT 500 air leak