How to Build a Small Misting Pump One Step at a Time

Let's take a look at the demo diaphragm pump I build and add some more options.

First, the pump above has a couple options on it.

  1. Input Solenoid
  2. Input Gauge
  3. Output bypass/regulator
  4. Output Gauge

Two of these options are the begining of control for a misting pump, the regulator and solenoid.

But first let's take a look at the basic diaphragm pump and see what can and can't be done with it. What are its limiting factors for misting?

Diaphragm Pump Discriptions Diaphragm Pump with Plastic Fittings

Pumps © Misting

Diaphragm Pump with Plastic Fittings Diaphragm Pump Bottom Showing Pressure Switch Wires Diaphragm Pump Head With Plug Diaphragm Pump Head Pressure Switch Inlet Port

A basic diaphragm pump by itself typically has a built in pressure switch. Depending on the pump application there are different pressure ranges. We will be working with a high pressure diaphragm pump. This type of pump typically has a maximum pressure of around 160 psi.

So one would think that a diaphragm pump with a ON/OFF pressure switch of 160 psi would work right out of the box. Yes it will, but !!!

What happens when you put a series of nozzles on the output of a diaphragm pump? Turn it on and the pressure will quickly rise to the pressure switch cut off point. You get your mist. The pump shuts down. Then the pressure in the line falls quickly (through the nozzles) and the pump starts up again. ON and OFF, ON and OFF quite rapidly. Not Good !!! About 1 time per second on average. The pump will die a quick death in about an hour or so, if not sooner.

What can be done?

First though would be to use a bladder tank to store high pressure water.

This is not a pretty picture but it shows how a bladder tank could be incorporated into a diaphragm pump mist solution. It shows several important mist system design concepts.

  1. Diaphragm pumps can lift (suck) water out of a bucket, etc. if needed. Blue bucket in the back. The lift is not real high, 3 feet max.
  2. Water will be pumped and stored in the blue bladder tank for delivery to nozzles.
  3. Diaphragm pump internal pressure switch can be used to cycle pump ON and OFF - without short cycling.
  4. Plastic fittings can be used, barely. 150 psi is right at there max. working pressure point. There are better plastic fittings on the market that have a 250 psi working pressure.
  5. The plastic tee with the ball valve is the output to the nozzles. The other end of the plastic tee loops around to the bladder tank inlet.

This bladder tank concepts works but it's not a real clean solution. Meaning there are inherent problems. The first picture above is a better solution and cost is about the same. But even it has issues. We will work through them all step by step.

Below is video of a bladder tank setup working.

<a href="">LinkedTube</a>

The top picture setup has several advantages.

  1. Pressure can be regulated. 140 psi is the recommended default setting.
  2. Regulation gives you the ability to run the pump continuously. However diaphragm pumps are not continuous duty rated pumps.
  3. Build in pressure switch them becomes your high pressure safety.
  4. Solenoid valve is used stop water flow through the pump on the OFF cycle. City water will travel through a non-operating diaphragm pump.

So this concept works but it also has some inherent problems.

The issue is when you shut the pump down. On the OFF cycle there is still high pressure in the lines. This pressure will slowly reduce as the water flow through the nozzles.

As the pressure reduces the mist becomes poor. The nozzle starts to spit larger droplets of water. Eventually just a stream of water will come out the end. Not the fine mist it was designed to put out. Things get wet.

In some applications this is OK. If you have a wet application like Hydroponics a little spitting my not be a problem.

If you have a dry application like humidification, spitting is generally not acceptable.

So what can be done?

The next step in mist pump design is to incorporate a dump valve. A valve that dumps the high pressure nozzle line water to drain on the OFF cycle. This valve is used to relieve the high side systems water pressure to 0 psi. Don't worry, not much is wasted, maybe a couple ounces.

There are several way to incorporate a dump valve. Each is a stepping stone to greater control and better operation. Each costing a little more. Finding the one that works for you is the goal of this web page.

The normally open dump valve.

This is the least expensive and the least complicated. The pump system ends up having two solenoid valves. One N/C, normally closed and one N/O, normally open.

The N/C in on the input, city water side. The N/O is on the high pressure output, misting nozzle side.

Both solenoids are powered when the pump starts. The input valve opens up, the pump starts, the output valve closes. The output close so water goes to the nozzles, not to drain.

When the pump stops, power to the solenoids is removed, the valves reverse postions.

The input valve closes. This is important. Water will flow through a diaphragm pump when it is not running.

The output valve opens. This also is important. This is the dump cycle we are after. When the valve opens high pressure water quickly dumps to drain. This reduce the nozzle supply lines to 0 psi. Again, it dosen't dump much water. It doesn't take much to reduce the pressure to 0 psi.

When the nozzle supply lines are reduced to 0 psi the nozzle check valves can to there job. They snap shut and prevent dripping. Just what we are after, no drip.

<a href="">LinkedTube</a>

This is a pretty straight forward system and work well. Electrical wiring is easy. Everything is powered at the same time. Everything shuts off together.

Does it have any drawbacks?

Yes it does. They could be considered minor depending on your application.

On the OFF cycle the N/O solenoid valve on the nozzle lines is open. If the OFF cycle lasts for an extended period of time the lines can drain. Ideally the check valves in the nozzles will hold this back. However, on an extended OFF cycle they will eventually drain.

This is not a bad thing but it can lead to some issues.

When the nozzle lines (high pressure lines) are empty they have to be filled again. Part of this filling process is bleeding air out of the lines. When you bleed air you get erratic nozzle operation. In other words you get spitting, you get things wet. Not much but you will get some larger water droplets

Again, this could be fine if your application is wet. But if not, you will have to read further.

Solenoid Control

The next step, the step to prevent nozzle line drainage.

We need to shut the N/O solenoid back closed again. This will keep the water from escaping, keep the water in the nozzle lines where it belongs.

This is fine because the solenoid valve has done it job. It has relieved the water pressure. The nozzle check valves have snaped shut. Why not shut the dump valve to eliminate any drainage.

When nozzle lines are full there is no air in the lines. Thus no spitting of the nozzles when operation resumes. When the pump starts water quickly rises to full pressure. An immediate quality mist is the result. 

So now we are at the point where we need control. We will need timers and relays and a control box. We will need an electrical diagram and operational instructions.

Don't worry, it not all that bad. I will step you through it.

Back to shutting off the dump valve.

At this point you begin to realize that a N/O dump valve is not a necessity. It can be a N/C valve. We are putting in control. In fact that is what they generally are, N/C. N/O valve are hard to find. They are also more expensive.

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