pressure compensated adjustable flow control valve... that shares return line with motor? 2

[reductive]

Hello

I was going to control a saw using a pressure compensated adjustable flow control valve, however it will require 3/4" or 1" return hoses for my desired flow.

I believe the "excess flow" port on the valve (which is also pressure compensated) needs its own return line directly to the tank. So this means I would need two 3/4" or 1" return lines, one from the motor and one from the valve... My question is whether there is a way to run a single return line to the tank

I was planning to use this type of valve,

https://www.northerntool.com/shop/t...92sH5MTx4g8yyWaIHMBoCn-kQAvD_BwE&gclsrc=aw.ds

If someone could tell me with certainty that it either does or does not require a separate return for unused flow

...Assuming it does, is there another type of valve or combination of valves that allows marriage of dumped flow and used flow? This is the main question.


...I am thinking i might need to use an electronically controlled valve of the type in the link above, located at the pump, so the excess flow circuit is back by the powerhead, so the system acts more like having a variable displacement pump. Then the trigger on the tool is just a 0 - 12 VDC controller. More expensive and adds a failure point, but would probably be pretty cool.

THanks for your time. And yes, this is for professional, commercial use! NO DIY!

 

[hydtools]

You can T the bypass flow to the motor return line. Make sure the motor return is sized to handle total flow that goes in to the flow control and not cause excess back pressure for the motor seal. Will not be a problem.

Ted

 

[reductive]

You can T the bypass flow to the motor return line

I was hoping so! Then I got worried that the slight backpressure of the 25'+ return line to tank (properly sized) would start some sort of fluttering or pressure build...

do these pieces of information change anything?:

*the motor is reversible
*both the work port and the excess port on the valve are pressure compensated
*the motor will be stopping and starting often

I'd be concerned that with a pressure compensating dump port on the valve, say i only crack the work port... Does the valve know to keep priority to the work port? Pressure in the return line will not cause the motor to start backwards when i crack the work port?

Again thanks. You might remember my asking about this same problem around this time last year. I never did figure out what a "metered land spool" was! Seemed like something that would have to be designed, whereas the valve above is relatively cheap, and while weighing in at 8 lbs, will hopefully give good control and will *hopefully* return to zero with a heavy enough spring.

Presumably I can just tie the return from the motor, the case drain from the motor, and the dump (excess flow) port on the valve into one large return line? No check valves or anything?

this is the valve:

http://www.brand-hyd.com/wfdata/files/install/valves/FC_Installation_Sheet.pdf

Again thanks for your time

 

[hydtools]

The pressure compensated priority flow control gives priority to the control port.
Why a reversible motor? A saw cuts in only one direction.
The forward delta P across the motor, even with 'cracked' valve, will turn the motor forward.

Ted

 

[reductive]

why a reversible motor

because i got a high performance motor for very cheap and it happens to be reversible. it's a small, 8000 rpm rexroth axial piston fixed disp... if you're bored here's the lit:

https://dc-us.resource.bosch.com/me.../industrial_hydraulics_5/pdfs_4/ra-a91001.pdf

i tried looking through that document for allowable pressure on outflow port during operation. it seems fine, however

i might want to throw a check valve after the motor so it doesn't get confused during minimal throttle?

...ok this just in, the FC51 valve that i've been looking at does say in some places, though not in others, that it is a priority type valve. this is quite important i think. the "priority" type valve ensures that the motor only turns one direction. that sounds right. i am almost ready to buy more parts. i should use hard lines from the work port on the valve and from the outlet on the motor to where the excess port tees back into the return line.

(here i am checking my own comprehension: if the excess port is loaded and doing work in another circuit, and then the work port is cracked, does the "priority" type valve cause a momentary drop in pressure in the secondary work circuit while the primary circuit loads? does the higher pressure circuit have to be first in the series? none of this applies to the system i am working on now. just in general)

also i'm wondering if the "pressure compensated excess flow port" on the valve i was talking about is misinformation. don't know that there's any compensation going on at that excess port if compensation is going on at the work port. they just mean that another work circuit can be connected to the excess port, or that it can build pressure... idk if its actually "compensating"

im confused again maybe ill wait until next spring and try again. i think im getting somewhere though

thanks again

 

[reductive]

i think it is a lie that the excess port on the valve is "pressure compensated" and i think that since only one port can possibly be compensated in this type of three way, single spool valve, it is therefore a priority valve.

im a beginner at this though so idk

 

[hydtools]

https://www.brand-hyd.com/Products/Valves/Flow_Controls/FC_0-30_GPM/

This is information from Brand Hydraulics about their FC51 valve.

On edit: get the valve without the optional reverse flow check valve so that flow cannot go from controlled port to inlet, then the motor cannot run in reverse.
Ted

 

[hydtools]

What kind of saw?

How do you turn it on and off, start and stop it?

Ted

 

[Stoolpe]

Your idea with a fixed pump and a priority valve will work.

However i'm not sure it would be the most attractive solution for commercial/profesional use.
If you are using the saw at anything else then full speed you will problably have a lot of losses and heat generation in the hydraulic system.
if we are to think about the environment and the electric bill.

maybe a varible pump with load sensing, or a closed loop circuit is a better choice. Dependent on the use/application.

It is always important to think about start stop for a motor. Maybe a braking valve or a check valve/anticavitation valve is neccesary for the motor to stop in a controlled manner.

"...I am thinking i might need to use an electronically controlled valve of the type in the link above, located at the pump, so the excess flow circuit is back by the powerhead, so the system acts more like having a variable displacement pump. Then the trigger on the tool is just a 0 - 12 VDC controller. More expensive and adds a failure point, but would probably be pretty cool."
All the flow that you doesnt use from a fixed displacement pump will be losses and heat generation in the hydraulic system. Problably better off using a actual variable displacement pump.

I believe the "excess flow" port on the valve (which is also pressure compensated) needs its own return line directly to the tank. So this means I would need two 3/4" or 1" return lines, one from the motor and one from the valve... My question is whether there is a way to run a single return line to the tank
No problem. You can use one return line from motor and priority valve.
Since you have a motor with external drain which should have its own line to tank with as low pressure as possible.
Connection T1 or T2 on page 12 in datasheet.

 

[reductive]

...its a large chainsaw. you run it with the "fc51" type of valve we have been talking about, which is incorporated into the handle of the saw. these valves are made nearly identically by a number of manufacturers, who all describe it differently, some incorrectly, hence my confusion about that. the saw will have a centrifugal clutch on it so the motor shouldn't be seeing too much shock, i can configure the clutch to disengage at whatever rpm.

i have an electronic open/closed valve that i can use at the powerhead to open and close the circuit to the saw, which will be 25' of 1/2" and 3/4", and then the valve in discussion is part of the *cough* handheld saw, which might not end up being handheld, it could be part of a processing system


might put a cat on the small 4 stroke gas engine... should be cleaner than a 2 stroke at least, and a lot quieter

i have a couple variable displacement pumps that are more in the 50 - 75hp ballpark, i wanted to get the smaller 25hp system working with a fixed disp pump before i try building a bigger system with a variable disp pump. it is probable that i will be asking about ways to control the load sense var. disp. pumps in the next year or two

i have an oil cooler w fan

anticavitation valve makes sense, idk if it will be necessary, the motor should be able to stop very quickly when the valve is closed

i was going to tee the case drain into the larger return line

...i asked about the types of triggers that are used on handtools last year, hydtools said to use a "spool with a metered land", which i assume is sort of similar to what i am using here. never did figure out whether such a thing could be an off-the-shelf part. i think most/all handheld tools are run off of relatively small fixed displacement pump, open systems. a var disp and/or closed system would be cool, but if the tool is 25' - 50' away from the pump, it seems like electronic control would be necessary

thanks again for any discussion is helpful. i think i have a whole plan now, i have some minor fab and assembly to do, my prime mover is a 26 hp kohler gas or propane.

ill be monitoring temps and pressure. it'll be a while before i get the thing built but i have it mostly figured out and i have most of the components

 

[hydtools]

The CS11 is the largest handheld chainsaw we made. At one time it ran a 43 inch bar. An advantage of the hydraulic drive is the relatively low spinning inertia resulting in low capacity for kickback for a handheld chainsaw.

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

Ted