Simscape Fluids 3-way directional valve (IL) spool displacement

Hi All,

Starting with the question:

My QUESTION is:

Been the valve parameters

Spool travel between closed and open orifice = 0.005m

Spool position at maximum P-A orifice area = 0.0045m

Spool position at maximum P-T orifice area = -0.0045m

Why do I need to apply a spool displacement of +0.0045/10 (0.00045) m to reach the maximum flow on P-A? Shouldn't be 0.0045m?

And here the model parameters:

I have a very simple implementation of a 3-way directional valve (IL) as below:

in which I have the follwing parameters:

And the PS sine that acts over the spool have the following parameters:

After that, the results can be observed below:

Answer 1

[Shivam Gothi]

Hello @Flávio Luiz,

As per my understanding, you are trying to figure out why the displacement “S” of (S = 0.0045/10) causes the maximum flow rate in the positive displacement path, instead of S being 0.0045. (S = 0.0045).

To clarify the above confusion, let us first understand the relation between the opening area of orifice (“”) and the flow rate.

The flow rate is directly proportional to “”. Due to displacement of spool in either direction, say positive direction, the "” increases and it increases the flow-rate in “P-A” path. But due to positive displacement of the spool, the “” for “P-T” path reduces and so the flowrate in the ”P-T” path reduces.

Now moving ahead with the question: “What is the relation between the spool displacement (S) and A_orifice for both the paths “P-A” and “P-T” ?

Refer to the below paragraph, taken from the documentation of “3-way directional valve (IL)” block:

https://www.mathworks.com/help/hydro/ref/3waydirectionalvalveil.html#mw_8629c3da-0428-4f86-8102-ecd050610293

Considering the parameters you have entered for the Valve parameterizations

The equation of A_orifice for path “P-A” is :

And the equation of A_orifice for path “P-T” is :

`

To visualise them graphically, right click on the block “3-way directional valve (IL)” select Fluids > Plot Valve Characteristics. The plot shows the Orifice area versus spool position

I have plotted it for your case, as attached below:

You can see that when the displacement is (S=0.0005), the path “P-T” closes completely and flow becomes zero. On the other hand, the orifice for the path “P-A” is still open and thus allowing some flow of fluid (as seen in the screen shot of scope as attached by you).

As converse to it, when the displacement becomes (S = -0.0005), the orifice for the path “P-A” closes completely and flow rate becomes zero. On the other hand, the orifice for the path “P-T” is still open, thus allowing the flow of fluid (as seen in the screen shot of scope as attached by you).

At displacement (S=0), both the orifices are equally open and so, we can observe equal flow-rate in both the paths “P-T” and “P-A”.

If you want to reach the maximum flow-rate on path "P-A" for spool displacement of 0.0045m, change the “Spool travel between closed and open orifice” property of the “3-Way Directional valve” block to “0.009”. After making this change, the plot of “A_orifice” vs spool displacement (s) becomes:

Therefore, we can see that when the spool displacement is 0.0045m, the “P-A” path orifice is completely open and thus ensuring maximum flow-rate at "P-A" path

I hope it resolves your query !

[Flávio Luiz]

Thanks!