Bad information from supplier or is it me ? 3

[xtal01]

I can't thank you all enough for your help!

I have one question left but my "gut" feeling is that the factory engineers may be giving me bad advice.

Just to review, I am planning on using a Brand Hydraulics EFC ( electrical proportional control valve ) to set the rate of lift / lower on a simple forklift cylinder.

In the power up mode, I will use it as a three port valve.

In the gravity lower mode, I will use it as a two port valve.

On the manual version of this valve ( FC51 ) you can simply block the EX port ( excess flow port ) and use it as a two port valve.

On the Brand web site I read:

2-PORT- The 2-port (2P) option is a modified version of the standard 3-port EFC. This option lets the
customer use the control flow port while the excess port is plugged. A special compensator spool was
designed to eliminate hunting that can occur between pressure compensated valves and pumps. To use the
EFC 2-port a pressure compensated pump is required. The 2-port can be converted to a 3-port (by
removing the EX plug), but it will not have the same characteristics as the standard 3-port. (See chart on
next page for 2-port EFC)

After reading this, I checked with Brand. The Engineer at Brand says I can ignore this and just order the standard EFC valve.

Hmmmm .... so why even have this option at all? Does this not tell me that I "need" to have this if I am planning on using it as a two port valve?

Maybe I am just reading too much into this but I just don't understand why they would give you a "2P" option if you don't need it.

Can you guys straighten me out please!

I have attached a diagram of the flow up and down through my circuit.

Mike

 

[hydtools]

You can just use the three port valve and externally block the EX port to have a two-port flow control. Brand makes the comment that if you order the 2-port valve you need to use a pressure compensated pump. You will not be controlling pump flow. You will be controlling cylinder exhaust flow which, in your case, will be essentially constant pressure flow like that of a pressure compensated pump. You do not need the special valve spool to prevent pump hunting. There will be no hunting as the cylinder will not be trying, as a pressure compensated pump would, to constantly compensate pressure.

Ted

 

[xtal01]

Ted .... YOU ARE INCREDIBLE!!!!!!!!!!!!

If you are ever in VT, I owe you a meal!

I have been trying all day to get this answer from the factor ... I have about 10 e-mails going back and forth with them.

I can breath again! This is exactly the answer I was searching for.

One possible problem the factory pointed out. They said when lowering the pressure from my CF port may unseat my "load check" and cause my load to drop.

I was "hoping" that with an open end ( assuming the filter is not blocked and minimum resistance from the solenoid valve ) back to the tank, the return line would have less pressure ( should be almost none ) than line coming out of the cylinder.

If this is going to be a problem, I can put a valve in just under the load check to make sure it does not open.

Any thoughts on this?

THANK SO VERY MUCH AGAIN !!!!!!!!!

Mike

 

[hydtools]

I would expect the pressure on the cylinder side of the load check valve to always be higher than the pressure of the FC side of the check valve during flow out of the cylinder. Flow goes from higher to lower pressure. If you want additional check valve closure assurance use a spring loaded check valve.

Ted

 

[xtal01]

Ted .... again awesome!

You read my mind ... I was just thinking to myself "I bet there is a spring loaded check valve with say 50 or 100 lbs of pre-load in it.

I have to ask ..... with your expertise in this and other subjects ( I looked up some of your other posts ) ... do you own a supply shop or are an engineer for a company or a professor at a university or ???

You can't imagine how very appreciative I am of all your help! You could not have done this project without your help.

I will post pictures of the lift ( or a link to it ) when it is complete.

Thanks again .... Mike

 

[hydtools]

BSME and 35+ years pneumatic and hydraulic tool and system design, retired.

Good luck with your work.

Ted

 

[Compositepro]

The little pink stars at the bottom of every post is there so you can show appreciation.

 

[xtal01]

Thanks! .... I did not realize that.

I will definitely star the post!

 

[kiwitom235]

Hi All. OK I may be wrong in my assumption but I am pretty sure you cant block the EX flow port unless you want to blow your relief valve (wasting energy and causing heat). Remember this is pressure compensated priority flow, so if the EX port is blocked and you restrict the flow on the CF port to zero, the pressure build up on the EX port will cause the valve to further force flow to the EX port (pressure compensating) and blow the relief at its set pressure. I think the EX port should be connected to Tank, this way the excess flow goes to tank at a much lower pressure than the relief setting and thus wasting less energy/heat. Otherwise you could just use a simple 2 port pressure compensated flow control valve and excess flow gets blown through relief. hydtools what do you think?

hydtools is correct in relation to the check valve, you dont have to worry about the load dropping as the check will always be seated during lowering.

 

[hydtools]

kiwitom235,you are correct if the flow control was being fed by the pump which is a fixed displacement pump. A 2-port flow control would force excess flow through the relief. In this case the cylinder is pushing flow through the flow control with the EX port blocked at a fixed pressure less than the relief setting and the flow control will control flow without forcing excess through the relief. I am assuming that the load coming down is the same or less than the load that went up and the relief valve is adjusted to not relieve with the heaviest expected load.

xtal01 ?

Ted

 

[xtal01]

The original forklift was rated at 3000 lbs.

It can obviously go up and down empty. The forklift is fairly heavy ... even with just the mast and forks. I would say 1000 lbs.

I estimate my "average" load both up and down will be 300 - 600 lbs.

The maximum load this unit will see is 1000 lbs.

Again, here I am showing my total lack of knowledge in hydraulics. The original relief valve was set to about 2250 psi (according to the forklift guys). I "assumed" the relief valve was only to "protect" the pump and circuit from high pressure and I was not thinking of it in the operation of the unit.

I do remember before disassembling the forklift that the relief valve would unload when the mast hit its upper limit (and the motor not shut off till you released the valve handle). In my case, I am planning on shutting off the pump as soon as it hits its upper limit.

Thanks for all your attention to my unit!

Mike

 

[hydtools]

The relief valve's main function is to protect the circuit components. It is not intended to control system pressure, except when the pressure demand or creation threatens component failure.

Ted

 

[xtal01]

Good, so I got the relief valve correct.

Reading the last posts, I believe I do need to block the EX port when lowering (the way I have it in my drawing)?

This was actually the recommendation of the factory back when I was thinking of using the FC51 ( manual version of the EFC valve ).

The pressure from the cylinder lowering (and raising for that matter) will (should) never be enough to set off the relief valve.

I purchased two NOS ( new old stock ) control boards last night (EC4000A) .... $95 each ( as compared to $560 for the new version ... DEC5000 ).

I am just waiting on a quote from Motion Industries ( listed by Brand as my "local" distributor even though they are in the next State ) to get the valve on the way.

Thanks again ..... Mike

 

[kiwitom235]

Hi guys,

apologies, I confused myself a bit with the pressure compensated valve. For some reason I thought that with EX closed it would attempt to close off the other exit port to compensate.

circuit seems good!

Tom

 

[xtal01]

No apologies needed!

I truly appreciate you and Tom took the time to go through my circuit.

Now I just need to figure out how much flow I have and I can order the flow valve.

My new problem is trying to decided between an EFC12-10-24 and an EFC12-15-24 ... 10 or 15 gpm valves.

The problem is I am using the pump/motor off the forklift. I can not find any information on the GPM.

It is my own fault ... I don't remember how long it took for the lift to go full stroke ... then I could have worked it out.

The real problem is that looking at the valve curves (

http://www.brand-hyd.com/efc/catalog.pdf

) the worst case ( 8 gpm pump and 15 gpm valve ) would use only 33% of my 4-20 mA span for control. Even at best case ( 10 gpm pump and 10 gpm pump ) I would only use 58% of my span. Some of this is caused by the valve .. it only "turns on" at .3 amps ( assuming 0 amps is 4 mA and 1 amp is 20 mA ... .3 is 9 mA ... 30% of span).

I am probably over thinking this but I just know "good design practices" suggest you try to use the center 80% of your span for control. 30% of the span is used before the valve starts to flow ... this leaves on 70%.

I have attached a quick sketch I made to show where the "control" falls on the valve input. I am just afraid I will get a minimal control of flow if the total flow from 0 to 100 % is represented by 33% of the span.

Any thoughts?

Thanks once again .... Mike

 

[hydtools]

Your two best cases are with the 10 gpm valve, per your chart.

Connect the pump to a supply of oil. Measure the pump output as you manually turn the shaft, e.g. measure volume delivered by 10 revolutions.



Ted

 

[xtal01]

I think I can "guess" at the volume of the pump ( or do as you said and check it ).

It is a Cessna pump #20214 1TBP ... I can not find a reference to this pump but in other Cessna pumps the last number represents the displacement. On the 253XX series, the 4 represents 1.2 cu in/rev

Now my problem is how many RPM's the motor is? I know DC motor s are not set at a specific RPM but there should be a nominal max that I can use.

The motor is a Prestolite MKA-4005

I was going to order the 10 gpm version of the valve ... but then I thought 'what if my pump volume goes above 10 gpm"????

Thanks .... Mike

 

[hydtools]

So what if the motor/pump delivers more than 10 gpm?

Ted

 

[xtal01]

That is actually my question!

I guess I assumed (maybe wrongly) the valve would not handle more than 10 GPM (actually 11 if you look at the curve) and the relief valve would open.

Is this true or would any flow over 10 gpm just go to the EX port or ?????

Mike

 

[hydtools]

The valve is rated to output controlled flow up to 10 gpm. There is not a statement as to how much over 10 gpm you can input. Any excess over 10 will go to the EX port. In order to control flow, the input logically should exceed your controlled flow output or there is nothing to control.

How much flow so you want to go to the lift? I have not gone back in this thread to find out.

If your pump displacement is 1.2 cu. in. per rev, then the speed must be 1925rpm to get 10 gpm.

Ted