alternative to clamping for flow restriction

[boldfish]

I have an application where a sping loaded clamp is used to shut off flow through 1/4" PVC tubing. The problem is that this clamp is in the clamped position for prolonged time and the tubing eventually deforms and retains the crimped shape affecting the flow characteristics when unclamped.

Can anyone offer alternatives to clamping? I've considered a small manually actuated valve but have had no luck in finding reasonably costing alternatives.

Any help is greatly appreciated.

 

[Ashereng]

Just curious.

What is the process fluid that is flowing through the tubing?
How good of a control do you need?
What industry is this in?

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Albert Einstein
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[boldfish]

The process fluid is a water based cleaning agent. Application is home appliances - volume in the 10-100 thousands. Ideally I need completely off, completely on.

 

[electricpete]

It seems like a small plastic ball valve is one or two bucks at the hardware store. The tough parts I guess are the extra work to attach to your tubing and also stabilizing the valve body while the handwheel is turned (normally the pipe holds the valve body but that wouldn't work too well for flexible tubing).

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[JStephen]

Would there be alternate tubing that wouldn't have that problem?

 

[Ashereng]

How about:

1) Bigger hose. This way, even when distorted by the clamping, it will still give sufficient flow - assuming the distortion does not progressively get worse.

2) IV tubeing with lock, the type that hospitals use. Not sure if those things come in 1/4".

3) A valve - you can try to attach it to something solid so that when you turn it, it doesn't move.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[boldfish]

I've been searching tubing specs all morning thinking a tube change would be the easy answer. Without indepth knowledge or experience, it seems that a test scenario is the only way to determine how resilient different tubes are.

The clamping mechanism now is a pivoting, spring loaded finger-pull type clamp. I want to stay away from turning type valves. I thought there may be a supplier of small in-line pinch valves that somehow contributed to reshaping the tube into circular form when released. Hard to explain, but easy (for me) to envision what I'm looking for.

Again, this is 10-100 thousands quantity. I'm looking for a solution that only costs in the 10s of cents. You know every penny counts.

Thanks again for the suggestions.

 

[GregLocock]

Add a v shaped slide to the clamp, so that as the roller that pushes the tube closed, releases, the V comes up from underneath and squeezes the tube's sides in.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[griffengm]

Mostly curiosity on my part but why not use a solenoid? Or can you go with a different hose material with less tendency to take a set?

Griffy

 

[btrueblood]

Do a search for "peristaltic pump" tubing. PS pumps put the tubing used through thousands of pinch/relax cycles per day. Of course, this also is what causes such pumps to experience failures within 6 months of continuous use, even with the best available hoses. The PVC you are using will probably develop fatigue cracks in a fairly short number of cycles, even if you could get it to rebound.

You need to switch to a rubber (elastomer) material, more like EPDM, Santoprene, or even plain old surgical tubing. Any of these materials will give you many thousands, probably 100's of thousands of cycles, before fatigue cracks start showing up and the hose starts leaking. Medical types have switched to the PVC tube, because it is easier to get the material past regulators (fewer additives used in their manufacture) and also the tubes hold up better to sterilization. But the majority of med devices are used for at most a few dozen cycles, then disposed of.

If you really must have the PVC tube (perhaps for the transparency of the tube?), then do as Greg suggests (create a mechanical means to reshape the tube with each cycle), or wrap the o.d. of the PVC tube with a section of rubber tubing, and use a clamp that fits the new larger o.d. The rubber tubing will "bounce back" better after pinching, and hopefully keep squeezing the PVC back into shape for enough cycles to suit you. The PVC will only be obscured over a short area within the pinch clamp.

 

[boldfish]

Near the nozzle on a long hose is an injection point for a cleaning solution. The flow of the two fluids are distinct from their respective pumps and the flow of the cleaning solution is on-demand (on/off) controlled by a trigger that pinches the tube to block flow (an ingenious bypass system handles the overpressure.) This is merely a spring loaded device. There are no electricals and the desire is to not have to run a wire along with the hose simply for the operation of a valve. I thought there should exist a small (~5/32 in ID tube) pushbutton (mechanical, manual) valve, but searching the web, I came up empty. I agree, the simplest solution is a change to the tube, but this, for me, requires long term testing to determine set properties.

The method of use for this particular product is such that the hose remains pinched for all but maybe 10 minutes per month. Not quite the ideal situation for any thermoplastics.

The issue is not exactly cycles. More an issue of deformation set.

Thanks for all the suggestions.

 

[btrueblood]

Again, you can shorten your research time by focusing only on peristaltic pump tubing. These tubing materials are made specifically to be pinched and relaxed a number of times without taking a set, and to be as durable as possible in that application. Look on the Cole-Parmer website for more info.

 

[MintJulep]

Perhaps something like the valve used on cans of spray cheese (or hair mousse)? I don't actually know what they look like inside, but it seems about right.

Or,

The "bite valve" common on runner/biker/hiker hydration packs.

Or,

Push-pull valve typical of water bottles and dish soap.

Or,

Twist valve as on a bottle of Elmer's Glue or mustard.

Or,

The flip the little spout 90 degrees valve that used to be common on shampoo bottles.

When you need cheap, look too mass-market consumer goods. Go visit the supermarket for further inspiration.