reciprocating piston circuit 2

[subsearobot]

Hi experts!
I am designing a 'dumb' system (no external sensing or control signals) for an Antarctic core sampler. I need to raise and drop a weight repeatedly to hammer the core barrel into the sediment. This needs to happen under 2000' of ice.

I think I have seen a circuit (too long ago to remember) that causes a ram simply to cycle back and forth. basically, when the piston hits the end stop, driving pressure climbs, and this pressure is used to reverse plumbing with some sort of logic valve. No controller necessary.

Is this possible? can anyone point me to literature? I have googled "reciprocating" type searches with no avail. Sounds like simple automation, but I do not quite grasp it...

cheers!

 

[PNachtwey]

You are getting some incorrect information in these posts.

Gkranz, what is wrong with my calculations? Subsearobot is only using gravity to do his drilling. He doesn't have banks of accumulators and oil like you do.
Notice that I mentioned using vibration to liquefy the ground like your systems do.

Peter Nachtwey
Delta Computer Systems

http://www.deltamotion.com

 

[Gkranz]

Peter,

I never stated your calculations were wrong, as always you are way too thin-skinned when it comes to YOUR calculations. All our hammers are gravity drop and we do not use banks of accumulators as you suggest. And you are not going to liquefy 200kPa soil without a lot of dynamic force?

For over twenty years I have designed machines that drive objects into the ground, I think I know a little something about the subject? If Subsearobot is smart, he will go to the web site I suggested and learn how the pros do it to give him some fresh ideas and correct information.


Best Regards,
Westerndynamics.com

 

[hydtools]

Gkranz, it would be helpful for us other contributors if you point out the incorrect information and why it is incorrect.

In your book of knowledge you describe loss of impact at angles other than vertical as solely the result of increased friction. I would say the loss is due more to reduced effective drop height. At 45deg the drop height is reduced to 71% just from drop height reduction. 10% less than what is shown in your graphic on page 34. Just saying.

Ted

 

[Gkranz]

Hello Hydtools,

First, I did not write the Book of Knowledge, Mr. John White did that writing.

Quote - Impact energy transfer is not instantaneous. The time to transfer is small but finite.

Answer – No it travels about 2400 ft/sec., we tested with sensors at anvil impact and tip (toe tip) some 100 feet at the bottom of the pile.

Quote - Consider using regenerative flow on the down stroke, connecting the rod end to the head end flow. This will give you higher velocity for given pump flow rate since the effective area will be that of the rod area which is smaller than the piston area.

Answer – Not true, we do connect the rod flow to the blind end flow to keep from pulling a vacuum on the blind side and to keep the blind side accumulator small. Remember this is gravity drop hammers, not double acting cylinders. It would take too much energy, flow and a much larger accumulator to do this. If we were to take that approach we would use nitrogen to accelerate the hammer down.

Quote - The flow rate will determine the maximum travel speed of hammer, the bore and rod size of the cylinder relative to the flow and pressure will determine the rate of acceleration.

Answer – In a gravity drop hammer, rate of acceleration is determined by gravity and drop height, oil flow only lifts the hammer up. Over all blow count is determined by total cycle time with dwell about 0.3 to 0.5 seconds after impact of anvil. This is needed to stop, reverse direction of oil flow only, nothing more.

These are just a few of the incorrect assumptions, and you will not use a double acting circuit, it just does not work very well at all, too much energy loss. The calculation of shear is absent the friction factors of the ID and OD of the pipe, more incorrect information. Peter’s idea to liquefy ice is wrong; it just cracks and does not liquefy like soil. For 200kPa a gravity drop will impart more than enough energy (dynamics force) to do the job. If you want to accelerate the hammer, it is done with nitrogen on the blind side, not oil. The only concern I see is the pipe or pile diameter with the length of 500 meters. It is not clear whether the 8” hole is drilled to soil level then driving the pipe, and if so how deep does the pipe go after reaching soil level? I would consider driving the pipe (gravity drop) from the surface (through ice) to soil level and beyond to required depth of pipe for soil sample. Then vibrate out pipe for extraction, all done from surface. When pipe comes out, you cut in sections for removing, then vibrate next section up and repeat until soil sample is up. Saves drilling and you get to go home sooner?


Best Regards,
Westerndynamics.com

 

[hydtools]

Gkranz, thanks for the response.

Would it not make sense for you to make sure your company presents correct information even though Mr white is the author? You referred the OP to your site to get the correct information.

I suggested a gravity drop hammer as a better alternative to the OP's desire to use a cylinder driven hammer.

When the OP continued to wonder about doing a cylinder driven hammer I suggested the regen to get more hammer speed. I have no intention to described the full design of a hydraulic hammer. That is what I used to get paid to do. And he was not talking about a drop hammer lifted by cylinders. As you clearly know, that is a different animal. I think he should consider the APE hydraulic hammer.

That is a clever idea to load the vibrator eccentrics with cabide to increase mass without increasing size.




Ted

 

[Gkranz]

Dear Hydtools,

American Pile Driving is not my company, Mr. White is the president of his own company.

There is some good information on the site that could enlighten OP or provide different ideas. As with many web sites, information can be some what miss leading and you should know that further research would be wise, they call it the internet? Loaded vibros use Tungsten and lead not carbide as inserts.

I do not recomend OP use Ape hammers or anything else, just tried to steer him in the right direction to solve his problem. You can check out my company at westerndynamics.com to get some ideas of our work.

Best Regards,
Westerndynamics.com

 

[hydtools]

Gkranz,
My apologies.
When you said you designed their impact hammers I drew the wrong conclusion.

Ted

 

[EdDanzer]

Gkranz,
It is very possible to build a hydraulic hammer that will accelerate the hammer weight with the hydraulic cylinder. This reduces the length of the system and can provide a reduction in hammer bounce that is common in gravity or gas driven hammers. This reduction in bounce may reduce weld stress cracking in well casing and provide more energy efficiency driving.

When we did some accelerometer monitoring at the top of 6” well casing, the length of the 6” casing, the soil and the hammer design has an effect on the energy transfer rate so I’m not sure if the energy transfer rate is the same in all instances with different devices doing the driving. We have not done extensive side by side testing with competitive hammers to be able to provide good quality data and results but I will invite you to Tenino Washington to see this unit work even though you do not think it cannot.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[Gkranz]

EdDanzer,

Good to hear your input Ed. First, diesel hammers rarely bounce because of the pressure pre-load on the pile cap, only if they miss fire would you see this bounce. Most gravity drop hydraulic hammers on the market will bounce often, however we have a patented control valve that will prevent this bounce. The X-13 hammer I designed takes this to the next level by preventing pile cap breakage and reducing the ringing sound by some 20db level by pre-loading the pile and cap. The energy transfer is the same with or without the bounce, however the real problem is that with a bounce you will “catch” the lump and drive the hydraulic pressure as well as the connecting rod connection beyond limits and cause damage.

I did not say you could not accelerate a ram downwards with hydraulic fluid; it is simply very inefficient to do so. Your accumulators would not only have to be big enough to make up the difference in areas, but provide additional flow force for acceleration as well, about 20% more. In addition, your plumbing would have to be sized for this extra velocity flow, which may be fine for very small hammers, but a problem on large hammers. The larger accumulators used for acceleration require longer recharge times and more pump flows as well.

It comes down to size and cost, larger lump and or drop height vs. extra plumbing and larger accumulators. I would not consider hydraulic acceleration on such a small pile of 6”, simply (in my opinion) the hard way to do it. The X-13 hammer is patented because of its special way we pre-load the pile, no other hammer does this. I am working now on the next generation above the X-13 that will be even more efficient, and the X-13 is 88% efficient now as determined by pile analyzer tests we have done. Our X-13 hammer drop height is adjustable on the fly and we can get a 41 blow count at 5-foot stroke and up to over 60 blow count at 1-foot strokes. There is a video on Ape web page of the X-13 hammer during testing, if you would like to see it in action.

I do disagree with you on one thing, the energy transfer rate is between the hammer, pile cap and pile, soil does not affect this energy transfer rate. Soil does greatly affect the penetration of the pile as does pile size in square area and length. A 6” well casing sounds like water well operation, and I have often wondered why these guys have not tried new technology as they have been doing it the same way for years?

The next time (not sure when that will be) I run tests on the X-13, I will call you and see if you would like to meet me in Kent to look over the operation. You may get some ideas that could be useful in your operation. I visited your web site; it looks like you do some interesting work, looks good.


Best Regards,
Westerndynamics.com

 

[EdDanzer]

Gkranz,
I’m not sure we are talking the same bounce. The bounce I’m referring to is when the hammer contacts the anvil. We use a steel hammer and a steel anvil that sets on top of the well casing. The housing that contains the hammer, cylinder and anvil must weigh more than the hammer and the acceleration rate force to keep it (the housing) from jumping up when the cylinder accelerates the weight down. Without an almost non compressible fluid acting to hold the weight against the anvil the hammer will be bounce away from the anvil after contact. Just drop a steel ball on a steel plate.

We do not use an accumulator in our system! Just 16 gpm to raise the hammer and drive it down. The cylinder has a bore to rod ratio that provides the required acceleration force and speed to provide over 1G of acceleration on a 600 lbs weight in 10” of movement.

I would like to see your next test.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[Gkranz]

Ed,

Wow, that is like trying to drive a pile (casing) with a big ball peen hammer? I bet the ringing sound will break windows and wake up people for blocks around. Yes we are talking the same bounce, but years ago we learned not to do it that way. We use ductile iron for the hammer (slug) and anvil, about the same density, and more than half the cost to machine. We also use an anvil cushion of special material to absorb rebound from anvil and/or pile.

Or slug is 23” in diameter, 72” long and weighs 12,263 lbs. Our anvil is 23” diameter and 32” long, so we do not follow your hammer vs. anvil weight. To give you an idea of the X-13, performance, we drove a 100-foot long, 24” diameter pile into the ground 98-feet in just over 47 seconds. Yes I know our X-13 is an over kill for water casings, but we do have low head room hammers that work from a backhoe that will drive your 6” casing down 40-feet in under one minute, same technology (sort of) of the X-13 hammer.

Your timing is good, we just posted to our web page calculations regarding oil expansion you may wish to see, look under tech talk page. Again, good talking with you.


Best Regards,
Westerndynamics.com

 

[hydtools]

What is the VI of your example oil?

Ted

 

[Gkranz]

Ted,

It was rated at 150sus (ssu) 100 F, but you can see it changes with temperature ranging from 80F to 180F.

A good reason to design a system to run in a stable range much more narrow, 110F to 125F.

Best Regards,
Westerndynamics.com

 

[hydtools]

Temperature control and/or using a high VI oil, 150 or higher.

Ted

 

[subsearobot]

some great stuff here guys. thanks for the references and discussion.

I appreciate all of your thoughts. Gkranz, your pile driving experience seems quite vast, and I always appreciate an expert's opinion. That said, I believe that there are always more than one way to skin a cat, and value everyone's contributions here. Constraints dictate a design, and every application has different constraints.

For our system, I am isolating the valving from the impact forces/ vibrations. Not true for the ram, which is lifting the hammer upward, and releasing to allow gravity to accelerate the hammer to strike the anvil.

can you elaborate on the possible failure modes of the ram, and methods of mitigating these? Our unit will be operating in Antarctica, so failures will be problematic. That said, operational cycles will not be very high for the life of the system. (likely less than 1000 cycles).

cheers

 

[EdDanzer]

Gkranz,

It looks like you have accumulators in your pile driver, what do they do?

The noise does require hearing protection, but the rest of the drill rig is just a noisy.

One significant difference between pile driving and well casing driving is space. Our prototype is 50” tall, 19” wide and 21” deep and needs to be even more compact. The 600 lbs hammer takes up about 21” of that space. The anvil has a 6” pipe and hose sticking out of it for the spoils to blow out of the hole plus areas to pilot the casing so it is about 12” long. There has to be a seal system at the top so all the air and spoils exit out the anvil vent. The hammer appears reach a speed of about 60” per second at the end of the travel with 16 GPM input. We have not rented a high speed camera yet to actually measure the velocity at the end of the stroke.

Subsearobot,

The cylinder problems you will need to address are; getting the oil out of the cylinder so it does not act as a shock absorber, the impact of the rod stopping will extruding the piston seal over the piston, and the shock in the system will loosen up the plumbing and the fasteners on the cylinder and anchor.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com