Dash Sizes 1

[ayoung802]

So I have a hydraulic system with two cylinders that use a sequence valve. At the start I knew information about one cylinder that used an SAE-6 Fitting. Knowing that I picked a sequence valve that also used SAE-6 fittings, that could operate at the pressure and the flow rate I needed.

I've now got information on the second (larger and longer) cylinder and it has SAE-12 fittings. Does that mean I should change the sequence valve and first cylinder to SAE-12 fittings. I understand the dash 12 is a larger hose and with that there will be less friction, but I need a little guidence on what else to consider.

Thanks

 

[Bribyk]

Not sure what you're asking but check out the thread below.

thread71-232971

 

[hydtools]

It depends somewhat on the flow rate you use. If the flow rate remains at 5gpm or less for both cylinders you would not have to up-size your first cylinder and sequence valve.

-6 is nominally 3/8 tube fitting
-12 is nominally 3/4 tube fitting

Ted

 

[ayoung802]

Okay maybe I gave the post title the wrong name. For anyone that has questions about Dash Sizes the link I've attached should help clear that up.

My question is more based around why would someone make a part with a -12 fitting unless it required a -12 fitting. I don't think they would. So therefore I think I have to at least upsize the sequence valve to a -12 port to meet pressure/flow requirements. I shouldn't have to change the first cylinder -6 fittings becasue the cylinder doesn't require any more flow rate then that.

Can someone with hydraulic experience verify my logic?

I'm checking the flowrates and pressure of the entire system and if I find anything more out I will be sure to post it here.

Thanks

 

[hydtools]

Just because the second cylinder has a large port does not mean you have to deliver more flow. Deliver more flow only if the function requires it. Larger components may have larger ports because they may be operated at higher flows. It does not mean they must be operated at higher flows.

Need to know what you are trying to do in terms of system function. I have run larger cylinders at low flow only because I wanted high force at low speed.

Ted

 

[ayoung802]

Thanks Ted for your response.

I do want a higher flowrate for the larger cylinder. I went through the entire system and calculated the fluid velocity in each hose and pipe section and made sure to keep the velocity within an acceptable amount. A -10 will work for the larger cylinder.

The problem that I'm struggling with in my head is I need to go to the next size sequence valve to reach the necessary flowrates 18.7 GPM, but the valve only has -8 fittings. I calculated the fluid velocity for -8 and believe the fluid velocity is to high. Still the sequence valve claims to source up to 30 GPM. Is it okay for the valve to use -8 because it is only for a short run and then once outside the valve I will jump up to at least a -10?

 

[hydtools]

If the sequence valve is sending flow to the larger cylinder after the smaller cylinder reaches its limit, I would go to a larger valve and porting. You are right, 18.7 gpm is a lot of flow for the -6 ports you say are on the valve. -8 ports would be ok. -12 would be best for that flow. In my experience valve manufacturers claim higher flow capacities for a size than good practice dictates.

Ted

 

[ayoung802]

Thanks Ted,

I appreciate being able to bounce thoughts off of you.

Andrew

 

[AcesHighJoker]

I wanted to comment on this so I signed up for the forum.
Out of my own curiosity A question... is the larger cylinder doing work during its entire extension?
It is also possible to setup a regenerative circuit by pressurizing both the rod end and cap end of the cylinder at the same time. Thus your only displacing the area of the rod and you can get away with the smaller fitting sizes. After extension you can switch flow to cap end only and get the same force you needed when you selected the larger cylinder.
Just wanted to mention that, you might save some money.

Regenerative advance:
Speed(in/min)=v(Flow of pump in in^3/min)/area of the rod(in^2)

 

[ayoung802]

Thanks for the comment, but I'm not 100 percent sure what you mean Ace.

The larger cylinder will be doing work the entire extension because it is moving a load. Can you give me an example of an application where a cylinder wouldn't do work the entire extension because it still has to over come some smaller internal forces?

Also what do you mean pressurize both the rod end and cap end? If the cylinder is extending the cap end will be under pressure and the rod end will be returning to the hydraulic tank. Do you mean restrict the flow on the rod end?

Thanks

 

[hydtools]

In regeneration, both cap end and rod end of the cylinder are connected together. Flow from the rod end is added to flow to the cap end. The net operating area of the cylinder is the rod area and it acts to extend the rod. The rod extends at higher speed but lower force. You get rapid advance of the rod until it reaches higher load resistance. The sensed higher pressure causes a valve to direct rod end flow to tank and you get what you know as normal cylinder operation. It is a technique used to use lower flow rate to extend the rod to a load, then apply full force to accomplish whatever you are trying to do near the end of the stroke.

A full description of what you are wanting your system to do would help the forum help you.

Ted