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reciprocating piston circuit
2

reciprocating piston circuit

reciprocating piston circuit

(OP)
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!  

RE: reciprocating piston circuit

Use a motor/roller chain setup with a pickup on the chain to raise the weight.  The weight then free falls to impact.
Google Cyclone breakers.  It's simple and uncomplicated.  The motor runs constantly, no starting and stopping.  I am assuming the work in vertical so that gravity drop will work.

A problem with the cycling ram is if you don't allow dwell time at the point of impact, production will be very low or not at all.  Without dwell, impact transfer to the core barrel is low.

Ted

RE: reciprocating piston circuit

Wandfluh makes a valve that switches cylinder direction after an adjustable preset pressure is reached. We have built a prototype well casing driving hammer using this valve and a hydraulic cylinder. It works very well if you vibration isolate the valve from the frame.  This valve will provide enough dwell / hold time at the end of the sroke to tranfer the force better than just dropping a weight free fall. When a weight drops free fall in a casing hammer it bounces atleast once.

Ed Danzer
www.danzcoinc.com
www.dehyds.com

RE: reciprocating piston circuit

True, the hammer may bounce depending on how much initial impact is absorbed by the casing being driven.  The hammer will have settled before the lift picks it up and there is no rebound reaction into the supporting structure.

The hydraulic cylinder will experience a lift in the time interval between when the casing is impacted and the valve responds to return the piston.  The structure supporting the cylinder must be capable of handling this hydraulic lift.

Ted

RE: reciprocating piston circuit

Quote:


A problem with the cycling ram is if you don't allow dwell time at the point of impact, production will be very low or not at all.  Without dwell, impact transfer to the core barrel is low.
I don't understand this.  It is the kinetic energy that does the real work ( force*distance).  After the cylinder stops the kinetic energy is dissipated.  Dwell time doesn't do anything unless there is enough force to simply push through in which case the the lifting part is required anyway.
 

Peter Nachtwey
Delta Computer Systems
http://www.deltamotion.com

 

RE: reciprocating piston circuit

Impact energy transfer is not instantaneous.  The time to transfer is small but finite.  If the piston is returned too soon because of an early signal to return, energy will be absorbed by or returned to the hydraulic system and less will be transferred to the casing.  Delaying piston return too long after impact wastes time in the whole cycle with no benefit to the delivery of impact energy.  The dwell I am referring to is that short period of time from just before impact to just after impact to deliver maximum energy to drive the casing.  Just experience designing hydraulic breakers which are sometimes used to drive posts and pipes.

Ted

RE: reciprocating piston circuit

(OP)
Ted,
dwell time is not too large of an issue in this system for a couple reasons.  first, the entire package (hammer, HPU, control electronics etc) must fit down a ~500m long hole in the Antarctic ice that is 8" in diameter.  My pump must be pretty small. second,  I have 5 shaft  HP available. this of course dictates flow rate. cycle times will be at a best 3 times that of the free-fall time for the mass.

I was looking at a pilot operated 4-2 valve from hydraforce.  I would sense the pressure developed at the end-of stroke. pressure to raise the load will be less than full system pressure. This system has me a bit concerned, however.  I think there could be false readings such as when accelerating the mass upward at the start of the stroke. I like Ed's suggestion if I stay with the piston solution.  I am also looking into the feasibility of the chain system like you suggested.  And for due-diligence, I am looking at using an ACME shaft and a triggered half-nut.  All are fun solutions, I think simplicity will take the cake.

ED, I will look into the wandfluh valves- I used Wandfluh for another project recently, and was very happy with both their function, and the level of support coming form the US division.  Using a time delay eliminates false pressure readings.

thanks all!


 

RE: reciprocating piston circuit

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.

Ted

RE: reciprocating piston circuit

When I did the design for the cylinder driven casing hammer the goal was 2G of acceleration in a relative short (10") travel. The hammer weighs 600 lbs. The cylinder has a very large rod to bore ratio and required a special piston seal to keep it from shearing off when the hammer hit the anvil. 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. If you do not need higher number of hits per minute or high acceleration rates the rod can be smaller relative to the bore than what we did. Because of the high retract speed we use a pilot operated check valve to dump additional flow from the butt end of the cylinder. It is important to have a large enough return hose to keep the back pressure down for proper function.

Subsearobot, I doubt you can stand 3G's (three times that of free fall). The mass that anchors the cylinder will have to be 3.1+ times the weight of the hammer to generate 3G's of acceleration otherwise the cylinder will move not the hammer. Once the hammer strikes the anvil it will start moving, soon after the anchor mass will have to start moving down with the anvil. We tried 1/8" of free travel between the anvil and the anchor mass and had to increase it ¾" to make it perform better.

Ed Danzer
www.danzcoinc.com
www.dehyds.com

RE: reciprocating piston circuit

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.
That limits the ability to accelerate because the effective area on blind side is now just the rod area.  This may be OK IF the rod is big but then there isn't much gain either.  
 

Peter Nachtwey
Delta Computer Systems
http://www.deltamotion.com

 

RE: reciprocating piston circuit

Peter, the smaller area just increases the pressure requirement.  We don't know the system pressure capacity.  That will be up to subsearobot's design.  So far we just have generalities without specifics.

Ted

RE: reciprocating piston circuit

(OP)
Ted, I'd heard of regeneration circuits, but never had the requirement.  This seems like the perfect opportunity.  The piston (mounted rod-down) will release the weight at the top of the stroke, then drive down to retrieve the weight.  the downward stroke is a high flow, low pressure requirement. Once the weight is latched, I need the pressure to accelerate the load upward. coupled with my limited size requirement, which dictates a low-displacement pump, this will help tremendously.

System pressure may be quite low, dependent on ram choice.  We typically use Bimba 500s (500 psi).  they are quite cost effective, and *relatively* corrosion acceptable (cheap enough to change out at service intervals).  At this low pressure, I do worry about parasitic pressure losses due to my high flow requirements.  I still need to quantify.

This high flow req. brings me to another question, but I will start a new thread for that...

cheers all
 

RE: reciprocating piston circuit

If you are trying to get much acceleration out of a cylinder you cannot use regeneration with the valve I describe as the force required to accelerate the load will not allow much back pressure.

Actually you will use more pressure to accelerate the load in a short distance to even reach 1G of acceleration than you may realize. If you do a force and velocity calculation for your hammer weight you will see how difficult the application is.

 I doubt an off shelf cylinder will provide the life or performance you need to make a cylinder operated hammer be effective.

Ed Danzer
www.danzcoinc.com
www.dehyds.com

RE: reciprocating piston circuit

Ed , don't those hammer systems rely on accumulators?  Where would you put them in such a small place?    Hydtools first suggestion makes sense but the limit would be just the energy released when the hammer falls due to gravity.
I like the simplicity.  The big question then is how far must the mass be raised and how big must the mass be to impart the necessary energy on the ice.

Reaching 1g is easy if you just let the weight fall using Hydtools' idea.  Getting more than 1g is going to be more expensive.

What is really required is an estimate of how much energy the hammer has at each stroke so we can tell if 1g acceleration is enough or if more is required. Knowing the mass that is accelerated is important too.

 

Peter Nachtwey
Delta Computer Systems
http://www.deltamotion.com

 

RE: reciprocating piston circuit

(OP)
Peter,
This is the root of the question, for sure.

I have inherited this project form another engineer.  When I began, I checked many details, but one that I took for granted was the mass and free fall height.  Now I am checking this, intuitively, something is not correct.

I have based the design around 100# mass free falling (1g acceleration) a distance of 1 meter (~40").  The impact energy is significant.  (based on a 5" sched 80 core barrel, impact force is ~84000#)

The client (yesterday (!)) told me that the maximum shear strength of the sediment is 200kPa (29 psi).  I am still looking at how to equate penetration depth/ blow to this low shear number.  Now, I need some civil engineering advise!  I did a back of envelope calc, and if it is correct (which it must not be!) this impact will drive the core tube 160" into the sediment (neglecting friction etc).

cheers


 

RE: reciprocating piston circuit

The hammer system we developed does not have an accumulator. The 600 lbs hammer has a 1 ½" bore cylinder with a 1 1/8" rod and 10" of hammer movement with 16 gpm feeding it from a gear pump. The Wandfluh valve and the PO check are the only parts besides the cylinder required to make the system work. The total valve and cylinder package could be configured to fit in an 8" circle if length is not an issue. The well drilling casing hammer requires a very short complete system length.

It will take more than 40" of travel to reach 1G of energy if you are not providing acceleration force.

Ed Danzer
www.danzcoinc.com
www.dehyds.com

RE: reciprocating piston circuit

The impact energy is 333 ft-lb.  W*h = 100*40/12
How did you arrive at 84000 lbs impact force?

Penetration will depend on friction resisting the core barrel movement.  Friction force x penetration distance = work done against the friction force = impact energy.  Work = energy

Ted

RE: reciprocating piston circuit

How did you compute 160 inches?   You know that can't be right.

I am assuming the mass is free falling as in Hydtools' method.

If the pipe is very sharp then shear force 8*π*29 or about 729 lbf/in.   8*π is the circumference of the pipe and the length of the shear distance.  This distance is multiplied by the shear strength to get the force required as a energy as a function of distance.  Think of this like a spring constant where work or energy=(1/2)*K*x^2, the integral of f(x) dx.  The energy when contact is made is 100lb*1g*1m=3927in*lbf.  This is simple energy=m*g*h.   ( Mathcad works out the units for me).  This is equal to (1/2)*729*(lbf/in)*(Δx*in)^2.   Δx=3.28in which I think is very optimistic because no other friction is taken into account and the shear strength seems low.

Another trick is to vibrate the the machine.  It makes the ground liquify like an earthquake and softer.   Perhaps some motor with an eccentric weight can help but at 2000 ft down it would be bad if the machine vibrated apart.

 

Peter Nachtwey
Delta Computer Systems
http://www.deltamotion.com

 

RE: reciprocating piston circuit

(OP)
I found the impact force by assuming the pipe acts like a spring. 1/2 kx^2=mgh.  solved for x, then plugged x into f=kx. this assumes pipe sitting on bedrock.  I did this calculation for a buckling analysis. I did, however use this force in the shear equation where 160" was the result.  I realize this is erroneous, because once the tube moves, impact force is significantly reduced.  

Pete, this makes perfect sense, thanks.  work in energy, not force.  I have some frictional values, so I can refine a bit.

 

RE: reciprocating piston circuit

Subsearobot,

You are getting some incorrect information in these posts.  If you want to know how to do this job, go to American Piledriving Equipment, Inc web site and get some good information.  You are basically driving a pile into the ground; this site will have good information on how to do this.

I design all their impact hammers and just finished the X13 impact hammer rated at 12,000 lbs and blow counts exceeding 38.  Other than the size, what you are trying to do is pretty easy.  Also, forget an off the shelf cylinder, never will hold up.  Valves and cylinder are always custom designed for application. Good Luck.
 

Best Regards,
Westerndynamics.com

RE: reciprocating piston circuit

Quote:


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

 

RE: reciprocating piston circuit

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

RE: reciprocating piston circuit

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

RE: reciprocating piston circuit

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

RE: reciprocating piston circuit

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

RE: reciprocating piston circuit

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

RE: reciprocating piston circuit

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

Ted

RE: reciprocating piston circuit

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
www.danzcoinc.com
www.dehyds.com

RE: reciprocating piston circuit

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

RE: reciprocating piston circuit

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
www.danzcoinc.com
www.dehyds.com

RE: reciprocating piston circuit

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

RE: reciprocating piston circuit

What is the VI of your example oil?

Ted

RE: reciprocating piston circuit

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

RE: reciprocating piston circuit

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

Ted

RE: reciprocating piston circuit

(OP)
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

 

RE: reciprocating piston circuit

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
www.danzcoinc.com
www.dehyds.com

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