Intro text on building a small fluid pressure chamber?

[theycallmevirgo]

TL;DR

I'd like to design a small (1-2L) chamber capable of storing ambient-temp water under pressure for an indefinite time. Can someone recommend a good intro text?

As stated in the summary, I'd like to design a chamber to store water under pressure. Nothing too powerful - basically at the level of a super soaker, maybe a little higher. The trick is, I want it to be powered and controlled electronically. But, I come from electronics land and know nothing about the mechanics involved. Where should I start reading?

The simplest thing I can think of is, there are plenty of air pumps around. Is this simply a problem of physically putting an air chamber and a water chamber in one enclosure?

Thanks so much

Joe

 

[jrmichler]

The easiest way to start is to buy a Super Soaker. You will have the pressure tank, air pump, and a valve to let the water out all in one package. All the parts are engineered to work together as a system. Buy two and take one apart to see how it works. All for less than the price of a good engineering book.

If you want higher pressure than a Super Soaker, go somewhere else. That gets into dangerous territory, and we do not allow that here.

 

[theycallmevirgo]

The easiest way to start is to buy a Super Soaker. You will have the pressure tank, air pump, and a valve to let the water out all in one package. All the parts are engineered to work together as a system. Buy two and take one apart to see how it works. All for less than the price of a good engineering book.

If you want higher pressure than a Super Soaker, go somewhere else. That gets into dangerous territory, and we do not allow that here.

Let's save a few steps. I want to do an electronic version of this;

https://www.amazon.com/dp/B087D8XQM9/?tag=pfamazon01-20

Aside from the issues people had with build quality, I'm really unclear why I need to be messing with a manual pump when I could design a system that will maintain a precise pressure electronically. Whether I make some Bluetooth remote or simply put a dial on the unit is beside the point.

Even if I was a fan of buying things for the sole purpose of disassembling them (http://thereisnoaway.net/), I still don't see any reason to spend money when there are libraries with books in them.

 

[Baluncore]

Summary: I'd like to design a small (1-2L) chamber capable of storing ambient-temp water under pressure for an indefinite time. Can someone recommend a good intro text?
But, I come from electronics land and know nothing about the mechanics involved. Where should I start reading?

Everywhere. Engineering is a multidisciplinary field that requires experience and the analysis of failure. First get away from electronics.

1. Does the system need to be portable, or can it be fixed in place?
2. What minimum peak pressure is required?

 

[theycallmevirgo]

As I mentioned previously, I'm trying to emulate this

https://www.amazon.com/dp/B087D8XQM9/?tag=pfamazon01-20

Obviously, it's portable, but I'm afraid I don't know enough to specify minimum pressure with any confidence.

 

[anorlunda]

I think it would be much easier to pump water out at constant pressure, than to pump air in and maintain pressure as the tank empties.

But, you could use a portable air compressor provided that it could be set to a low enough pressure. 1 psi should be plenty. But since the commercial ones are meant for tire inflation, it is possible that they can not be set as low as 1 psi.

 

[jrmichler]

In Post #1, you want pressure similar to a Super Soaker. That's enough pressure to spray several 10's of feet - about 30 or 40 PSI. In Post #3, you want enough pressure to push water uphill about one foot. That's only enough pressure to get it into your mouth without having to suck.

We need to know more about you really want to do. Is it an electrified hydration pack? Or is it something else? If you tell us what your desired result is, we can help with the technical requirements to get there.

I still don't see any reason to spend money when there are libraries with books in them.

OK, so here goes: There is no one book that has everything you need to know. Look for one each book about:

Fluid dynamics. You will need books on statics, dynamics, and physics to understand it.
Basic electricity.
Pressure sensors.
Pumps.
Motors.
Relays. You will need enough electrical background to understand the need for the snubber diode.
Batteries. You will need enough electrical background to understand batteries powerful enough to drive pumps.

Or you can tell us what you are trying to accomplish.

 

[theycallmevirgo]

I think it would be much easier to pump water out at constant pressure, than to pump air in and maintain pressure as the tank empties.

But, you could use a portable air compressor provided that it could be set to a low enough pressure. 1 psi should be plenty. But since the commercial ones are meant for tire inflation, it is possible that they can not be set as low as 1 psi.

View attachment 304925

I considered this and temporarily dismissed it for the exact reason you mentioned, it might not be able to set to low enough pressure. Besides, I want something that will automatically restore pressure as I release water from the reservoir.

 

[theycallmevirgo]

In Post #1, you want pressure similar to a Super Soaker. That's enough pressure to spray several 10's of feet - about 30 or 40 PSI. In Post #3, you want enough pressure to push water uphill about one foot. That's only enough pressure to get it into your mouth without having to suck.

We need to know more about you really want to do. Is it an electrified hydration pack? Or is it something else? If you tell us what your desired result is, we can help with the technical requirements to get there.OK, so here goes: There is no one book that has everything you need to know. Look for one each book about:

Fluid dynamics. You will need books on statics, dynamics, and physics to understand it.
Basic electricity.
Pressure sensors.
Pumps.
Motors.
Relays. You will need enough electrical background to understand the need for the snubber diode.
Batteries. You will need enough electrical background to understand batteries powerful enough to drive pumps.

Or you can tell us what you are trying to accomplish.

Yes, I specifically would like to do an electrified hydration pack. Basically identical to the one in the Amazon link, but with an electronic system that will maintain pressure as I discharge water.

I'm fairly familiar with the electronic aspects of the problem. It's the reservoir itself (and attendant pump power requirements) that I don't know how to estimate.

Sorry if I was being unclear.

ETA: The other aspect of their system that I really don't like is that their reservoir is one unit with two bladders. From my preliminary reading, it seems like I should be able to make an air bladder that would maintain a constant pressure as a completely separate unit from the water reservoir. That way I could sell it as an aftermarket accessory for any hydration pack. The obvious problem would be finding a way to insulate the air intake, battery and PCB from leaks.

 

[jrmichler]

Before getting into the electronics, you need to figure out how you are going to move the water. The two ways that first come to mind are:

1) Push on the water using air pressure. You do not need a separate bladder if you pump air directly into the water bladder. Or, as you say, you can pump the air into a separate bladder.
Or,
2) You can pump the water directly.

Either way, you need to figure out the range of pressures needed. The lowest pressure is with the water bladder full, with the hydration pack adjusted to a high level, and a user that likes the nipple down low. The highest pressure is with the water bladder near empty, with the hydration pack riding low, and a user that likes the nipple up high. Fortunately for you, low pressures can be measured using units of inches of water. The vertical distance from the water level to the nipple measured in inches is also the pressure needed to push the water up to the nipple.

Then you need to know the flow rate while the user is drinking. You can measure this using a piece of hydration bladder tubing and a drinking glass. Measure the rate the water drops in the glass, calculate volume vs time, and translate into useable units. Usable units for small pumps can cubic inches per minute, cc per minute, gallons per minute, or liters per minute.

Add appropriate safety factors to the flow and pressure needed. Now you have the performance specification for a water or air pump. That performance spec will look something like:

(Water) (air) pump for XXX in^3 per minute at XX inches water pressure.
Battery voltage XX volts.
To be used outdoors, could get rained on.
Etc

You need to find a pump that meets your needs before concerning yourself with the electronics. After you find such a pump, whether water or air, come back and we will help with the next step. Hint: The next step has nothing to do with electronic controls.

 

[theycallmevirgo]

Before getting into the electronics, you need to figure out how you are going to move the water. The two ways that first come to mind are:

1) Push on the water using air pressure. You do not need a separate bladder if you pump air directly into the water bladder. Or, as you say, you can pump the air into a separate bladder.
Or,
2) You can pump the water directly.

Either way, you need to figure out the range of pressures needed. The lowest pressure is with the water bladder full, with the hydration pack adjusted to a high level, and a user that likes the nipple down low. The highest pressure is with the water bladder near empty, with the hydration pack riding low, and a user that likes the nipple up high. Fortunately for you, low pressures can be measured using units of inches of water. The vertical distance from the water level to the nipple measured in inches is also the pressure needed to push the water up to the nipple.

Then you need to know the flow rate while the user is drinking. You can measure this using a piece of hydration bladder tubing and a drinking glass. Measure the rate the water drops in the glass, calculate volume vs time, and translate into useable units. Usable units for small pumps can cubic inches per minute, cc per minute, gallons per minute, or liters per minute.

Add appropriate safety factors to the flow and pressure needed. Now you have the performance specification for a water or air pump. That performance spec will look something like:

(Water) (air) pump for XXX in^3 per minute at XX inches water pressure.
Battery voltage XX volts.
To be used outdoors, could get rained on.
Etc

You need to find a pump that meets your needs before concerning yourself with the electronics. After you find such a pump, whether water or air, come back and we will help with the next step. Hint: The next step has nothing to do with electronic controls.

This is exactly what I needed, thanks so much. But now I think about it, couldn't I simply calculate rate of flow as mass of water per unit time and determine work to be done by the bladder, given worst case scenario of tube pointed vertically upward? I mean, I'd have to find a worked example of work done by an air bladder but surely that would be in some undergrad text?

Thanks again

Joe

PS - one thing I neglected to add is that it should optimally drive water through an inline filter. That might simplify matters, if I recall correctly those have specified flow rates.

 

[Tom.G]

Uhmm...
... Please take into account how the user gets water when the battery dies!

 

[anorlunda]

It may be much simpler if you pump water at a constant mass flow rate rather than constant pressure. A positive displacement pump would not be sensitive to tank level, or to height of the outlet spigot.

Rather than calculate the minimum size pump and motor, why not just experiment with several? Experiments may reveal considerations you didn't think of.

 

[theycallmevirgo]

Uhmm...
... Please take into account how the user gets water when the battery dies!

The old fashioned way :). Plus, I'll obviously include solar charging.

 

[theycallmevirgo]

It may be much simpler if you pump water at a constant mass flow rate rather than constant pressure. A positive displacement pump would not be sensitive to tank level, or to height of the outlet spigot.

Rather than calculate the minimum size pump and motor, why not just experiment with several? Experiments may reveal considerations you didn't think of.

I was thinking the exact same thing. I was copying the original design too closely, but the main disadvantage with your suggestion is it might be a bit difficult to make it work with every existing system.

 

[anorlunda]

I was thinking the exact same thing. I was copying the original design too closely, but the main disadvantage with your suggestion is it might be a bit difficult to make it work with every existing system.

I can't quite visualize what you're trying to do. That post makes it sound like you will buy backpack water tanks with the squeeze bulb, then convert them to add solar panels, pumps and controls? Is that right? What are the added costs and increased benefits?

 

[theycallmevirgo]

I can't quite visualize what you're trying to do. That post makes it sound like you will buy backpack water tanks with the squeeze bulb, then convert them to add solar panels, pumps and controls? Is that right? What are the added costs and increased benefits?

No, no no, The purpose of the squeeze bulb is to maintain pressure on the fluid chamber so water is sprayed out of the feed tube. I want to replace the squeeze bulb with an electronic system. That way, I get

- precise pressure control

-automatically replace pressure as water is consumed

-optional remote (smartphone, bluetooth, etc)

-Optionally aftermarket accessory for _any_ hydration pack, depending on how I design.

I consider the bulb system to have many drawbacks, so I want to find a way to replace it altogether. Which is not to say I want to buy their units and "repair" them. I'm trying to design a solution that will fit other existing products, as many as possible.

 

[anorlunda]

-optional remote (smartphone, bluetooth, etc)

OMG. The last thing I want is to unlock my phone and start an app, to take a sip of water.

I already have an app to adjust the volume on my hearing aids. Sometimes it takes as many as 3 minutes to get the phone started, the app started, then for the app to connect to the Bluetooth hearing aids. If I told someone else, "Please hold what you want to say until I adjust my hearing aids.", they will certainly loose patience and walk away before 3 minutes.

I'm definitely old-fashioned, but my favorite designs all follow the KISS principle. Long live KISS.

 

[theycallmevirgo]

OMG. The last thing I want is to unlock my phone and start an app, to take a sip of water.

I already have an app to adjust the volume on my hearing aids. Sometimes it takes as many as 3 minutes to get the phone started, the app started, then for the app to connect to the Bluetooth hearing aids. If I told someone else, "Please hold what you want to say until I adjust my hearing aids.", they will certainly loose patience and walk away before 3 minutes.

I'm definitely old-fashioned, but my favorite designs all follow the KISS principle. Long live KISS.

Welp, that's why I said optional. But the app would only set pressure. After that you just open the valve.