How to maintain fountain height in SLC?

[ckchew666]

I'm writing a program using SLC 5/03 to control a fountain. I face a difficulty in maintaining the height of the water shot out by the valves. As a standard my valves can shot up to 2 metres. But in some of the patterns, the height need to be programmed so that it's maintain in 0.9 metres. My system only consists of Digital only. I'm sure any experience gurus here will have some ideas how to do this, right? Please give this newbie a word or two. Thanks.

 

[rsdoran]

Sounds to me like you need to use proportional valves and analog cards.

I can see making part of the fountain just shoot to .9 meters but not maintain that. That would be a flow control issue.

I hope someone can tell how to do another way.

Actually I think I retract that...will pulsing at .9 meters work? Seems you could (with experimentation) use timers to "pulse" the water to go to .9 meters and seem to maintain there.

Use a flip flop timer ckt..where its on long enough to get to .9 meters and off for a few milliseconds or tenths ..whichever is needed.

The problem I see here is getting it to actually "maintain" a specific height..it may pulse some unless you can get the timing just right.

 

[ed]

Why not just use an array of solenoids, each one in series with a pressure regulator set to the desired pressure.

 

[Peter Nachtwey]

Good Idea, but....

Why not just use an array of solenoids, each one in series with a pressure regulator set to the desired pressure.

Don't you mean in parallel? If in series then any shut valve would stop the whole flow.

If the valves are in parallel then two valves could spray higher than just one because there would be less pressure drop / flow rate.

I doubt if this can be pulse width modulated unless the valves are extemely fast. If you find valves that fast I would like to know.

 

[rsdoran]

Peter he was saying an array of solenoids each one in series with a regulator preset for certain pressure, not in series with each other.

I dont think the pulsing thing will work either, I think analog and proportional valves are the best shot.

 

[Bob O]

What is the diameter of the column of water and what pressure are you using? Are you trying to get laminar flow from your fountains?

Thanks,
Bob

 

[Mr Dave]

Using only digital I/O for controlling the fountain can be down but repeatability is out of the question. Water pressure alone will affect the height of the water.

To be able to control the flow of the water using proportional valves while maintaining a constant water pressure will give the best results.

 

[Steve Bailey]

If you're truly limited to digital I/O, then you might need to take a 'don't raise the bridge, lower the river' approach. Use your discrete I/O to control a mechanism that raises and lowers the valves.

However, when you consider the cost of the mechanism, you'll probably decide to re-evaluate your decision not to use analog outputs.

Another possibility would be a motorized pressure reducing valve. If the speed of the motor is slow enough, you can use a proximity switch to count the number of turns made by the motor, which will be related to the pressure.

 

[Tom Jenkins]

I'm going to confuse the issue with some fundamental fluid dymanics facts. The height of the water column flowing from the nozzle is dictated by the velocity of the water as it leaves the nozzle, period, end of story. (Go look at the fundamental ballistics in chapter one of your high school physics book - the same analysis applies.)

The velocity is dictated by the size of the nozzle and the flow rate of the pump. The pressure in the system is dictated by the resistance to flow created by the nozzle. Flow creates pressure - pressure does not create flow, contrary to popular opinion.

So, if you want to shoot the water higher, you need to increase the velocity as it leaves the nozzle. If you want to increase the velocity you need to:

A) increase the flow rate from the pump to each nozzle. For example you could use a VFD driven pump, which can be controlled with discrete outputs using the pre-set speed contacts available on most VFDs, or jog up and jog down inputs

B) or change the size of the orifice, using ed's suggestion or a modulating valve.

 

[Steve Bailey]

Tom,

I'm sure you didn't want to leave the impression that there is no relationship between pressure and flow. In my opinion, the statement that "flow creates pressure, not the other way around" is an oversimplification. It may be a good way to look at things when you're designing or sizing a pump for an application, but swim to the bottom of a pool and your ears will tell you that you can get pressure without any flow.

ckchew666 says he can get a height of 2 meters with his system as currently configured. I envisioned a set of valves connected to a municipal water supply. From the standpoint of his system, the municipal supply looks like an infinite reservoir at some fixed pressure. If he can reduce that pressure, he'll also reduce the flow rate (velocity) and see a lower column height.

 

[Tom Jenkins]

You are correct, Steve, that I was referring to a pumped fluid. Obviously, static pressure is a different energy source into a system. In that case a water tower or stand pipe are indeed essentially a source of constant pressure. In that case the flow through a given restriction will increase until the losses equal the available static pressure.


In the case of static pressure you can approximate the nominal velocity of spouting water:

V = C x Sqrt( 2 x g x h)

V = velocity in feet per second
C = orifice coefficient = 0.6 for a straight edge orifice
g = 32.2
h = height of water column = psi x 2.308

 

[jam4095]

fountain height change???

I did a fountain some years ago with 12 valves and 4 light banks. The customer wanted the same situation as what you are doing. I thought about going digital,with paralleled valves and flow controls, but I had 3 banks that needed to vary, so I went analog..when the customer viewed the end result he wanted so many changes..IE a little higher here...a little lower there..plus pressure changes at the manifold with different valves on created havic. I ended up all analog so they could get anything they wanted..plus some file moves to produce different fountain and light programs for different times of the year...At the end of the day I am glad they went the extra cost of analog, or it would have been a night mare...What they asked for on paper before the fountain was built and what they wanted to see after it was finished ended up being vary different..(especially with the mayors wifes' input..) So If you can talk them into it ...GO ANALOG!
Joe.

 

[ckchew666]

If you're truly limited to digital I/O, then you might need to take a 'don't raise the bridge, lower the river' approach. Use your discrete I/O to control a mechanism that raises and lowers the valves.

However, when you consider the cost of the mechanism, you'll probably decide to re-evaluate your decision not to use analog outputs.

Another possibility would be a motorized pressure reducing valve. If the speed of the motor is slow enough, you can use a proximity switch to count the number of turns made by the motor, which will be related to the pressure.

Steve,

Mechanism control is out of our mind. All the valves are already installed on site. Now only waiting for the panel and program to be installed at the site.

The diameter of the valve is 25mm from crytsal fountain. These valves have two nozzles, one shoting vertical and another shoting diagonal. Trying to look for the part number. If any of the gurus here came across this valves, please provide me the part number. I'm trying to deal with the vertical shoting height now.

Just to inform that these valves(vertical nozzle) have to operate in 0.9m, 1.5m and 2.0m depends on the patterns. Each pattern will last for about 2.5 minutes.

Thanks.

Regards,
CK Chew

 

[ckchew666]

Hi,

I've checkout the problem with one of my friends. He suggested that I use timer to control the on & off signal to the vertical valves. By doing this very fast, I can maintain the height of the water level at 0.9m or 1.5m as I wish. But this need to be test on site to see what is the correct timing to be use.

I'm not sure if this is a working method, any expeirence ppl here can clarify my doubts before I start programming? I'm affraid the 1746-OW16 can't take that switching. The fountain will be operating 24/7.

I'll be in big trouble when written the entire program and realize that it's not a working one at site!! Thanks.

Regards,
CK Chew

 

[ckchew666]

I'm going to confuse the issue with some fundamental fluid dymanics facts. The height of the water column flowing from the nozzle is dictated by the velocity of the water as it leaves the nozzle, period, end of story. (Go look at the fundamental ballistics in chapter one of your high school physics book - the same analysis applies.)

The velocity is dictated by the size of the nozzle and the flow rate of the pump. The pressure in the system is dictated by the resistance to flow created by the nozzle. Flow creates pressure - pressure does not create flow, contrary to popular opinion.

So, if you want to shoot the water higher, you need to increase the velocity as it leaves the nozzle. If you want to increase the velocity you need to:

A) increase the flow rate from the pump to each nozzle. For example you could use a VFD driven pump, which can be controlled with discrete outputs using the pre-set speed contacts available on most VFDs, or jog up and jog down inputs

B) or change the size of the orifice, using ed's suggestion or a modulating valve.

Tom,

Our system consists of 32 valves and 2 units of 1746-OW16. The lights are all hardwired - always on. How many I/O does a VFD pump will consume? Thanks.

Regards,
CK Chew