Scannivale Design

You have left out the single most important factor...

What is that Please explain ?

What is the maximum pressure you are dealing with!!!????

Dear Sir

Maximum pressure will be upto 5 in H2O.

5 inH₂O, what media?

The media is air.

If an array of pneumatic valves (SMC) is not acceptable, you can look at selector valves for chromatography (HPLC) for inspiration.

This would not be too hard to design but may require good machining quality. At this low pressure, plastic such as acetal or Delrin against stainless steel would be good.

Please advise for further assistance.

We need purely mechanical as well as hand operated switch. So, Please go through mechanical design only.

Del's idea is similar to the HPLC link provided.

We want design a scannivalve which enables individual pressures to be selected for measurement from up to 40 input pressures by a single pressure transducer.

Max pressure and media are not just important, I would say essential.

You are Right Sir.

The numbers of which are what, and in what units?

Sir

We need designing method of simple pressure selector switch / scannivale.

You left an other important information what do you expect ? or is it only an information about you design planning?

Sir

It is not a nick name. It is a simple pressure selector switch

Up to large number pressure leads are connected to a single manifold via a

similar number of small-bore rubber tubes which are normally

clamped shut. Any pressure lead can then be connected to the

manifold, and the pressure measuring instrument, by unclamping

the appropriate tube.

Where a large number of pressure measurements are to be

made it may be convenient to use a single pressure transducer

along with some form of pressure scanner or selector switch.

The Scannivalve is widely used for this purpose, but it is

expensive, and the principle on which it is based demands a

high standard of constructional accuracy.

I appreciate your humor but my question was justified. You should have written : I am short of ideas, I do not know how to design it, could I have a helping paw?

This last indication was not present. You only stated that YOU want to design a " replacement for a scanivalve". That was all.

In fact you should be glad Del made the effort to discover what you did not write.

Be careful his idea has a flaw but I let you discover it by yourself.

5" of water is very little pressure, a simple turned/milled nylon part with O rings would do the job...maybe I'll sketch something. Mind 40 is rather a lot of inputs. maybe go for a smaller number and then uses several of the selectors.

Del

You are absolutely right Sir. We can consider upto 20 tubes at a time. Please send the drawing immediately. If possible.

Thanks with best regards

MOHD. SAEED KHAN

Something like this would do, you could add a spring loaded ball in the top which located in small indentations in the lower part to give correct alignment.
Of course this is a manual valve....

Sir

The sketch is not clear. May I have a clear drawing for the purpse. Is it possible to E-mail to me.

No, It is not off topic. First I have go through this sketch. Perhapes this sketch will not serve our purpose.

It's jsut a sketch...an idea ... you should be able to start experimenting with the idea.

It doesn't pretend to be an engineering drawing and I'm not a mechanical design eng'.

I'm just trying to lend a paw.

Del

Thanks for your good advice.

"It's jsut a sketch...an idea ... you should be able to start experimenting with the idea."

Lots of ideas, a basic design, etc. etc.

This thread reminds me of an ancient American saying:

The coat and pants do all the work, the vest gets all the gravy.

Capiece ? Capiece !

A few modifications/improvements?

I await payment of tinned Sardines

No Sir

The sketch is not clear.

There is a rotation between the plates to connect the output port to one of the input ports.

Yes offcourse there will be rotation between two plates to connect the output port of the input ports.

Altarnatively you may choose the sliding system.

So, what is not clear?

You don't have to design a Scanivalve. You can buy them here at www.scanivalve.com .

We have used them in flight test operations on experimental aircraft sensing pressures as low as millimeters of H2O. They are very reliable and can scan at rates which allow the minumum settling and data aquisition times to be as short as possible. We have experienced sampling rates using a 48 port Scanivalve of 5 milliseconds per measurement.

Very true, however building one from scratch is fraught with potential disasters. That is why Scanivalve has few if any, competitors.

There are used Scanivalves in the test equipment market and most MT&DE houses will rent you one for much less than aquisition costs.

They do require a delicate touch and skill in sequential programming. The data aquisition system must ignore transients and sample the "stabilized" pressure level at least several times before moving on to the next port.

IMHO designing, building and debugging your own scanivalve would be a challenge even for an experienced Scanivalve engineer. Sliding seals require micron finishes and I noticed in one submission the contributor missed the necessity to vent the moving port before transferring to the next sampling port which of course would alter the readings at each subsequent port. Especially if going from a high pressure sample to a low pressure sample in the 5 millisecond sampling window.

At the risk of sounding up myself I think that is tosh!

You only need fancy equipment if you are trying to scan fast..the original question said n'owt about speed or automation.
At 5" water pressure an O ring will seal fine even against a piece of injection molded plastic... I've done it on a commercial bit of respiratory measuring kit no need for micron finishes. (ok it's an ugly and obsolete instrument...)

Del

True my feline friend. Plastics will give you a very smooth surface, for a while anyway until contaminants do their dirty work.

Scanivalves are usually required where multiple near simultaneous pressure measurements are required such as sampling airflow over the wings of an aircraft as it translates from flying to a stalled condition. The information is fleeting so rapid aquisition is imperative.

You'll also see scanivalves employed in determining pressure distribution field about a Formula One race car when at speed. Especially during those fleeting moments when it is being buffeted by being directly behind a competitor, something which is hard to simulate in a wind tunnel.

I guessed the questioner selected a scanivalve for such transient measurements and as such responded with my answer but you are correct, the original question "said n'owt about speed or automation" My apologies..

My apologies..
none required ... I'm not sure the questioner knows what they want .

Del

Yes, we want measure the pressure over the airfoil surface and various other models in the wind tunnel test section in our laboratory.

"Yes, we want measure the pressure over the airfoil surface and various other models in the wind tunnel test section in our laboratory"

Now you tell us???

It wasn't a secret.

Why not in your first post???????

Offcourse , It is not a secret. Actually CR4 is the Engineers Forum, every experienced engineer can understand the application. I am very surprised that The people does not know the application, they are writing the comment. So, Please don't mind be stay with forum and write the comment.

Offcourse , It is not a secret. Actually CR4 is the Engineers Forum, every experienced engineer can understand the application. I am very surprised that The people does not know the application, they are writing the comment. So, Please don't mind be stay with forum and write the comment.

You are being quite rude to this community. We all have been asking you to explicit your application. This is not a charade game!

If you know you need a Scanivalve, go by one!

If you are running a wind tunnel for airfoil charaterization, stop being cheap and buy a scanivalve.

If you say on the other hand you need a selector valve with manual actuation, the application may be quite different. I know you know, so I will leave you understanding what I mean.

If you expect people around the world to interpret your miscommunication as professionalism and expertise, you are fooling yourself into self importance and are not going to get mutch help.

My apologies..

If you feel like this. It is just a matter of understanding, to save precious time and intelectual.

ROTFLMAO!

Yeh..EXACTLY

To save my precious time and intellectual could have provided the following at the begining.

a) Pressure.
b) Scan speed (you still havn't answered this)
c) Manual or automatic. (you still havn't answered this)
I despair
Del

See post #25:

''We need purely mechanical as well as hand operated switch. So, Please go through mechanical design only.''

So speed is not a factor or he would hire hyperactive operators.

Pressure is 5''H₂O.

Your sketch fits the bill!

What a wonderfull Cat you are!

Hello, Del

Thank you very much for your efforts. The sufficient parameters have been provided. No need for extra parmeters.

Thank you once again.

MOHD. SAEED KHAN

"MOHD. SAEED KHAN Offcourse , It is not a secret. Actually CR4 is the Engineers Forum, every experienced engineer can understand the application."

All CR4 engineers are NOT running wind tunnels, measuring a few inches of water gage pressures and using scannivate valves everyday and some not in a life time. Be grateful for what we tried to do with little information and that given grudgingly.

You have worn out your welcome with many if not most of those posting to this thread in an effort to assist you and you withheld information we asked for to better understand your application.

Don't be surprised if future threads started by you are ignored by many who posted to this one.

You need to offer your apologies to each and everyone for your superior attitude and ungratious manner. This would have been a private message otherwise. SS

Actually to be fair...the seal requirement depends to some extent on the flow capacity of the pressure source. e.g. Say the pressure was just a sealed 1cc cube at 5"H₂O then any leakage, and indeed the act of connecting any measuring ststem would lose significant pressure.
Or, assuming a reasonable reservoir of pressure or flow of the media then the seal isn't quite as critical.

Del

Ah ha !
My design can be simplified...

The bottom plate can have simple plain holes drilled through it for the inlet ports! ( they should be chamfered very slightly on the upper surface )
The upper plate with the outlet hole can have the O ring...so there is just one O ring! That's less machining and less cost.

The O ring should be nice and fat and fit snugly in it's recess, O ring manufaturers give figures for tollerancing and compression etc.

The 'hose tails' for the inlet could be steel tube just pressed in.

Maybe make both parts of Nylon or one of brass one of nylon...whatever...blimey if I had machining facilities I'd have made one by now.

Del

<...blimey if I had machining facilities I'd have made one by now....>

What, and marketed it under the KrisDel^TM label as well?