Water Volume delivered to Glass

The article is based on my observations and discussions with people involved daily in window cleaning and as such I am not setting out to provide definitive answers, but simply trying to get people thinking about how they work and why.

What works for one person may not work for another. The article is about water volume as delivered to the glass, and how much water is needed. Is a fast flow always best? Or should we look at lower flow but greater volume?

Everything that we do as a supplier is based around water delivery to the window, and as such I have been fortunate to gain many insights over the years. I would like to share some of these and look forward to continuing to gain and pass on my knowledge and experiences.

I will touch on some of the following points during the article.

  • Jets (pencil-fan-size-number)
  • Hydrophobic glass/hydrophilic glass
  • Water management/pumped systems
  • Fast water
  • Volume to suit the job
  • What role does a pump regulator play?
  • UK/EU/US technique

Firstly let’s touch on the different techniques used in the UK, the EU and the US. WFP use in the UK and to an extent in the EU has developed around the need to manage water. Pure water is produced away from the work site using static RO/DI systems. A water tank or barrels of pure water are then transported to the site.

Water management carries through the whole ethos of the cleaner where the tendency is to use 2mm jets and brushes with a void - this contains the water within the brush head, the jets help to pressurize the system by creating a restriction at the brush head. Restricting the water with the use of jets reduces the amount of water drawn from the system.

The US cleaner has fewer concerns over water management allowing the use of a stand alone on demand RO/DI trolley system which connects into an external water supply at the customers’ site. Pressure is now created by the mains water source and the amount of flow becomes dependent on the RO membrane.

In turn, the tendency is for a larger jet or fan jet. In some cases, up to 5mm and the larger jet creates a completely different water pattern when delivered to the glass rather than a smaller jet. We would see a cascade effect with a wider stream of water running down the glass. They are also more likely to use a full flock bristle brush with up to four water jets or fan jets spreading the water wider.

In a nutshell, the US cleaner is delivering water with lower pressure and flow but the same and occasionally a greater volume of water to the glass than their UK counterpart. This higher volume of water delivered to the glass can mean fewer passes of the brush are required to get a good clean. The volume of water then can be more beneficial than running the pump at maximum with high pressured fast water.

What impact than do the jets have in regard to water volume? There is always debate on the forums regard to Pencil and Fan jets. Like many things with WFP, there is no absolute right way - only the right tool for the job at hand. This may mean that the ability and flexibility to alter the jets size and type job to job will be very useful.

Hydrophobic and hydrophilic glass reacts differently to each other. Water will bead up on the hydrophobic glass but naturally sheet on Hydrophilic glass. Fast water from a Pencil jet will generate a very different water pattern to a fan under high pressure and this effect will become more noticeable. The pencil jet can be useful to those who need to conserve water as the restriction allows for less water to be used because it is under pressure. However, this fast water hitting the glass hard is bouncing the water around the glass in all directions. This may lead to spotting as the water runs off the glass so quickly that the glass is rinsed only where the jet hits the glass. For those that rinse with the brush off the glass, this fast moving water hitting the window as a jet can create spotting as dirt is pulled from the area surrounding the window by splashing. A brush with an internal void allows the water to be contained within the brush head reducing the risk of splash back up the window and pulling dirt off the surrounding brickwork.

The pictures below show differing rinse fields of different sized jets on Hydrophilic glass. The picture on the left shows a very narrow rinse field meaning more passes are required to get a good rinse. The picture on the right, however, shows a larger ID jet with a wider rinse field. The effect of a wider jet and greater water volume means fewer passes are required. 

Image reproduced by Courtesy of J.Racenstein

 A fan jet will allow for water moving more slowly and give a wider cascading effect down the glass and in some cases this cascade effect is useful, in particular with Hydrophobic glass, where a pencil jet will see beading of the water droplet and a narrow field of rinse as seen in this video example of Hydrophobic Glass vs. Hydrophilic Glass https://www.youtube.com/watch?v=4SORg3AQ8nw

When rinsing hydrophobic glass, a slower flow rate with greater volume is likely to see better results and less spotting as the glass cannot fail to be rinsed due to the sheer volume of water. On hydrophilic glass water will naturally sheet, making the rinse easier as the water will naturally want to spread out over the glass.

There is an argument then when rinsing hydrophobic glass that greater water volume but travelling slower is advantageous. So this begs the question, what role can a pump regulator play and does the same volume of water need to be delivered to the glass for both the clean and rinse cycle? I’m aware of users who want as much flow and volume as possible at all times, and in effect, I am proposing just that, delivering a higher volume at lower pressure. Equally, there are those who prefer a lower flow when washing then increasing it for rinsing. The ability to vary the volume delivered can provide a great deal of flexibility.

There are occasions when water mains pressure is not sufficient to generate the required flow with an on demand system. Fitting a pump before the RO is one solution to this, and another advocated is to use DI only as less pressure is lost than through the RO membrane. Once a pump is fitted do we need it to run flat out to generate good volume? We have seen that using pencil jets while running the pump hard will. 1) Mean fast moving water hitting the glass hard and 2) high pressure is created in the system.

So what is the effect on the pump and system of this fast moving water? An average 100PSI pump generating 5.2 litres (1.4 US gallons ) a minute is going to draw 6 – 8 amps an hour so in theory a pristine 75AH battery will run your pump for 10 hours? Actually, the answer is NO - as the pump draws current from the battery the load increases and the faster the voltage will fall so, in reality, the time to completely exhaust the battery is less. How much less depends on a number of factors. Not least that the faster the pump is running the less efficient the motor becomes as it heats up. The high pressure created also puts a strain on the hose line – connectors and pump motor. Over a prolonged period, this set up is likely to reduce the life of the battery, pump and other components of your system, with increasing downtime and repair costs.

Considering increasing volume yet at the same time slowing the water down will have the effect of reducing the strain on your system, meaning less downtime. This equals more time working together with increased earnings. Higher volume could mean less time spent per window as less time is spent per window it becomes possible to use the same tank of water to do the same work. How then do we best reduce the water speed, increase water volume and manage the battery? This is where a means to control the water speed is of use. There are a number of ways to achieve this: Manual taps, Pump head recirculation and an electronic controller. Some choose to work with a pump running flat out with the system operating at maximum pressure. My views on this are well stated and as such there is no need to repeat them here. It works for those who choose to work this way but it would not work for all.

My question here is simply, is this the most efficient way of working? Do you need the water flowing fast at all times? In this case, there is 4 – 5 litres (1 to 1.3 US gallons) a minute hitting the glass.

While this volume of water can be useful in particular with Hydrophobic glass, is it necessary? When we begin to see that the volume is the key not how fast the pump is working. It is beneficial to the whole system to reduce the pressure, either by means of changing the jets or slowing the pump with an electronic control.

As we establish that the ability to alter water volume delivered to the glass is important, we also need to look at the means to achieve this. There will always be situations where a pump is required even with on demand systems as the water mains may have low pressure. It is about having the tools available when you need them.

An electronic pump controller as mentioned in my article in WCM last year does far more than just adjust pump speed. It will also monitor system pressure, display battery voltage and stop the pump when water stops flowing plus help manage water resources. It is not necessary to run a pump at its maximum to achieve high volumes of water as we have seen there are a number of ways to do that.

If we work on the principle that the pump does not need to be working at maximum why not regulate the pump speed and reduce the current used and thus extend the life of a battery? Slowing the pump will also reduce the pressure in the hose line and connectors - less pressure, fewer failures reducing downtime and costly repairs. A controller allows effective variation of water flow meaning you can adjust the water delivered to the window using a lower volume for a clean and increasing it for the rinse cycle.

I am sure some will say running the pump flat out means you work faster but my question is this, if it takes 19 seconds to clean a window how can having fast water change this? There are physical limitations as to how fast an operator can work.

There is an argument here that higher water volume may help you work more effectively as the increased water volume and less splashing is likely thus reducing the risk of spotting and may require fewer passes of the brush.

You can use manual taps or even pump head re-circulation but for me personally, if used in isolation without a pump control, the pump is working at maximum at all times generating maximum pressure in your system as discussed above. The more I understand the cleaning process, the clearer the need to deliver the correct volume of water to the glass becomes, the more I question why to run a pump at its maximum all the time. The differing techniques show there is more than one way to achieve high-quality results while working efficiently and maximising earnings per job.

Working with high volume will not suit everyone nor indeed should it be used on every job. Managing water can be critical, particularly if you are using a backpack or have a limited supply. However in some cases slowing the pump but increasing the water volume may give you better results while still managing the water as it allows efficient working practice. There is a case for combining tools to give you the versatility to tackle all jobs and still be able to adjust water volume to suit. There are some good quality manual taps on the market - aquadapter and aqua tap to name two. Combine these with different jets and a pump regulator for the best of all worlds. The taps can help give you ease of stopping/starting the water. The control will simply see a Dead end and stop the pump. A controller gives the benefit of managing the pump battery, system pressure and water supply and stopping the pump well before the pressure switch is activated thus protecting the whole system while giving maximum versatility.

Increasing the volume of water to the glass will increase the amount of water used marginally however it is far less than some may imagine. The increase can be as little as 0.2 of a gallon (less than a litre) a minute. However, this is balanced by the fact that you will be able to rinse using fewer passes. In reality, then water use is not going to change. Plus because we slowed the pump to point where it only works as hard as required, a slower pump means less water is drawn from the tank.

In summary, water volume delivered to the window and the ability to alter this volume is going to give you a versatile system to suit a wide range of jobs and challenges. This can be done even where water management is important. Windows cleaners worldwide are able to share best practice and offer insights allowing all to examine if they are working as efficiently as possible.

I do not pretend to be a great authority but I do believe in sharing knowledge and getting people asking questions. I hope you have found this interesting and perhaps have you thinking about your own working methods. When it comes down to it there is no absolute right way - only the right way to suit a particular job. As discussed even this will vary person to person. What is critical to business success is having the right tool at the right time, however, you choose to work - have fun out there.