[TheForge] Power hammer questions/Frosty

Thu Apr 10 01:43:01 2003

Frosty,
I have a semi complete Krause type hamer. Last weekend I mounted a larger
power cylinder and had to replumb the Krause style valve for the larger hose
required by the new cylinder. As an experiment before I redo the valve,  I
thought I would try the Massey circuit and valve you described.
I connected top to top and bottom to botom ports. I then tee'd into these
two lines and inserted a ball valve. Just as you said, when the valve is
open, the ram or slave cylinder does nothing. When I close off the ball
valve, the ram rises and falls in the opposite direction of the power
cylinder.I dont have a check valve so the ram stays on the bottom die when
the valve is reopened.All as you described and pretty predictable.
I should now celebrate or brag(?), but all is not well just yet. After a few
good hits, the ram started to "short stroke". The ram stroke shortened and
did not come down or go up completely.I believe this is due to the fact that
my balance valves -the kind described in  Mark Krause's pamphlet, are not
large enough. I have grooves ground on the piston rods(double ended
cylinder) at the point where when the piston is at top and bottom dead
center, these grooves  will extend past the  seal   to allow air in or out
of the circuit.  Because the rod is moving up and down so quickly , these
grooves are not in position very long and I believe the "excess air" from
the larger power cylinder binds up the slave cylinder. My question to you
/and or the group is does this make sense? Can someone tell me the approx.
size of groove needed? My power cyl. is 5" dia and 6 in. stroke. The slave
is 2.5 in. dia. and 10 in. stroke. The displacement ratio is about 2/1, I
believe.The gear reduced speed is about 275 strokes per min.
I tried  to follow your response to Bob Schade below. If the ram cylinder is
mounted so that  the cylinder cannot fully extend before the top die meets
the bottom die, should you be concerned about knocking out the bottom end of
the cylinder?
I believe it is a good idea, as you said, to have more rather than an
inadequate amount of displacemnet . If this is done, you should be sure the
balance valves are of adequate size.

I did not try using holes at the equator of the ram cylinder for balancing
the system(ala Massey) but I like that idea as well because I believe you
can move more air that way without making grooves in the cylinder rod which
could weaken the rod.
I really appreciate your info on Masseys. This valve  circuitry may really
simplify the home built self contained  hammer.
As a post script to my speculation that the balance valve son my hammer are
inadequate, I did enlarge the grooves and the hammer seemed to be working
much better . I only ran it a short while before one of my welds broke, so I
dont want to say I am sure this is the fix. After some repairs this weekend,
I hope to give it another try.
Thanks for any comments. Do we have a fluid power technician in the group?
Regards,
Bob S.

----- Original Message -----
From: "Jerry Frost" <[email protected]>
To: <[email protected]>
Sent: Tuesday, April 08, 2003 7:10 PM
Subject: Re: [TheForge] Power hammer questions/Frosty

>
>
> ----- Original Message -----
> From: <[email protected]>
> To: <[email protected]>
> Sent: Tuesday, April 08, 2003 2:22 PM
> Subject: Re: [TheForge] Power hammer questions/Frosty
>
>
> > Frosty,
> >
> > What do you mean by "oversizing the pistons"? Thanks.
> >
> > Bob
> >
> >
>
> Basically making them larger than necessary. One ratio I remember for a
100
> lb hammer is: 6" compressor piston and 4 1/2" ram piston. To maintain the
> 1:1 ratio, the compressor stroke is half that of the ram piston.
>
> If I used 8" compressor and 6" ram pistons for the same weight it would be
> what I'm calling oversized. The displacement ratio ensures proper stroke
> length on the ram so it doesn't knock the end out of the cylinder.
However,
> there is almost twice as much ram piston as necessary to do the job and so
> the peak pressures would be halved.
>
> I'm not so much advocating this as a good idea as saying if you're not
sure
> how much piston to use, make them oversize just so long as the
displacements
> match.
>
> Frosty
> ------------------------
> If it ain't forged
> it ain't real.
> Wrought iron is.
> The FrostWorks
>
> Meadow Lakes, AK.
>
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