how to build hand tool trigger, pressure compensated valve for "feathering" at actuator 1

[reductive]

Hi all, first post. I'm building a small hydraulic power unit (25 HP) for hand tools, chainsaw, auger, etc

i'll be building the tools myself, one reason, besides cost, is because i'd like to run higher pressures than small tools are generally rated for and smaller hoses. a 4000psi chainsaw with 3/8" hoses versus the typical 1500-2500psi devices that require more flow and larger hoses...

anyway my question is about developing a trigger mechanism. my first project will be open circuit, fixed displacement. i am looking at pressure compensated flow regulators (which dump excess flow), this is the best thing i can find for use as a "trigger" that would be part of the handle of the tool. they look like they'll be stiff though, i was wondering if anyone knew of any type of soft trigger type mechanism that i could use as part of the tool in a 4000 psi open loop system

...another thought is using a variable displacement pump, which i think would allow me to use for the trigger at the tool either a remote electronic servo control or a simple orifice valve (which still aren't readily available in anything other than a knob, which would be poor control for a chainsaw or an auger) which would rely on flow regulation and pressure compensation integral to the pump. variable displacement pumps with integrated control (in the low price range) seem to stop at around 3000 psi though, whereas 4000psi fixed displacement pumps can be had new for under $150...

sorry if my wording is a mess. i'm just asking about how to build a nice trigger for a ~4000+ psi, 7.5 GPM hand tool... i could buy an old impact gun or something like that for cheap and then see about taking it apart and repurposing the trigger and handle, although these are generally rated for lower pressure than i want to use.

thanks

 

[akkamaan]

Not to know what your preferred prime mover option is I'd look into an AC motor with Variable-frequency drive, VFD together with a fixed displacement pump. No dumping of flow and electronic speed control.

 

[reductive]

Not to know what your preferred prime mover option is I'd look into an AC motor with Variable-frequency drive, VFD together with a fixed displacement pump. No dumping of flow and electronic speed control.

I'm using a gas motor, rpm will be fixed or very limited in range (1800 - 2800 rpm).

I can't really imagine the electricity bill of frequently starting and stopping a 25 hp electric motor

 

[hydtools]

You should use 1/2 inch hose for 7.5 gpm, not 3/8. The handheld tools I designed and built ran on 2000psi, 8gpm systems. Remember that with chainsaws it is speed that cuts.

What advantage will you have at 4000psi, but still 7.5gpm? The majority of handheld tools run on 2000psi, 8gpm systems. There are tools that run on 2000psi, 5gpm systems that use 3/8 hose.

Ted

 

[IRstuff]

Is this for work? DIY posts are not allowed

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[reductive]

You should use 1/2 inch hose for 7.5 gpm, not 3/8. The handheld tools I designed and built ran on 2000psi, 8gpm systems. Remember that with chainsaws it is speed that cuts.

What advantage will you have at 4000psi, but still 7.5gpm? The majority of handheld tools run on 2000psi, 8gpm systems. There are tools that run on 2000psi, 5gpm systems that use 3/8 hose.

Ted

I believe that standard hose sizing charts suggest a max flow rate of around 7.5 GPM for only 3/8" hose. I just thought it would be nice to have a smaller whip carrying around a chainsaw or whatever else, and you can get small motors that are rated for 4000psi, so the whole idea is scaling pressure up and flow down (within reason), it will allow for more compact systems. With a chainsaw, speed isn't everything, and the sprocket can be sized up quite a bit, you use the dogs when cutting, and I'm trying to build a a significantly higher-than-normal-torque saw, still around 2k or 3k rpm i think. ...And obviously 4000psi at 6 gpm is going to do more work than 2000 at 8.

The BUMMER is that 6000 psi pumps are around 20 times the cost of 4000 psi pumps. We'll see what happens

WHat were the trigger mechanisms like on your tools? A regular pressure compensating flow regulator with a spring trigger? At this point I am thinking i will just use a simple p.c.f.r., but loading the adjustment lever with a spring and making it work like a trigger. this seems barbaric. any tips there? thanks

Is this for work? DIY posts are not allowed

Really? This system (and/or its successor) will be used for (commercial) work at least a little bit.

 

[hydtools]

The reason for using 1/2 hose is to keep return line backpressure down. That backpressure is reflected against the motor dynamic seal and trigger spool seals causing drag and high trigger movement force that is exerted by the opertor's fingers. The tool, in the end, is actuated by hand. Handheld tools are generally flow tools not pressure tools.

Ted

 

[reductive]

The reason for using 1/2 hose is to keep return line backpressure down. That backpressure is reflected against the motor dynamic seal and trigger spool seals causing drag and high trigger movement force that is exerted by the opertor's fingers. The tool, in the end, is actuated by hand. Handheld tools are generally flow tools not pressure tools.

Thanks, that helps a bit. I know return line is supposed to be bigger. I am thinking about 3/8 pressure and 1/2 return instead of 1/2 pressure and 3/4 return. I say "handtools" but this includes an auger with large handlebars, which would need loads of torque. an auger though would be less concerned with small hoses and a gentle touch, low-feedback, progressive trigger. im still just focusing on the chainsaw trigger. it seems like there are no off the shelf parts that will work like a trigger on a properly designed hydraulic saw or other handtool, and i suppose the closest i could get with "off the shelf stuff" i.e. *not* making my own pressure compensating valve body from billet... would be to use a var. displ. pump and put the remote control at the tool. this is much more costly than fixed pump etc

 

[hydtools]

Make a spool with a tapered metering land.

An auger like the Little beaver?

https://www-littlebeaver-com.cdn.ampproject.org/v/s/

http://www.littlebeaver.com/product...lebeaver.com/products/hydraulic-earth-drills/

Or this Stanley?

https://www.stanleyinfrastructure.com/products/earth-augers

Ted

 

[reductive]

Make a spool with a tapered metering land.

see now im lost. i have little to no idea what this entails. i have very little fabrication capabilities to be honest, i can bolt things together and get some welding and a little bit of machining done. i'd be interested in what this type of valve you suggest is, and i will educate myself on it a bit, but again, im kind of looking for off the shelf parts

yes like those augers, for dirt or with a woodsplitting cone on it. an auger can have a deadman on/off switch or the stiff, bulky flow regulator would be fine for that. but a chainsaw (for woodcarving for example) would benefit from a softer, progressive trigger. even impact guns need a progressive trigger.

 

[hydtools]

See the Stanley CS05

https://www.stanleyinfrastructure.com/products/chain-saws

Or Reliable Equipment

https://rentaltoolsonline.com/relia...jeI1ysTSx6I3fwGTWtoPQpJ3CrYsSoIRoCNkUQAvD_BwE

Ted

 

[reductive]

See the Stanley CS05

you're saying that is the type of valve that these saws use?

I am looking at using one of these Link mounted as part of the handle of the tool. lengthening the lever on the valve and giving it a spring return to zero, if i'm lucky it might work well, right? if i only need to use 0 - 8 gpm then the angle of adjustment is small enough that that should work for a trigger

 

[hydtools]

Yes.

Sure, that priority pressure-compensated flow control would work since you are looking for some bolt together solution. It will be a heavier solution compared to the designed valved handle.

You also do not need to jump to 3/4 inch return. 5/8 inch would do.

Be careful with the auger torque. It could beat the crap out of you and wind up the hose before you can let go of it.

Ted

 

[reductive]

the motors im looking at for the auger should make at least (continuous) 400 - 450 ft-lbs, e.g. a 25 lbs parker motor with high shaft loading tolerances... so yes, even with a 3' handle it could get very violent. this is why a trigger that returns to zero if released is important.

electronically controlled compensating 3 way valves are attractive, the trigger would be nice at least, however i doubt the response times of these is very good, and my hopes are low for getting information on that.