Pressure Dynamics within Water Fed Pole systems

Pressure Dynamics with Hydraulic water pressure in WFP

Following on from an excellent article in the July issue of WCM (Myth Busting)
Pressure Flow and water fed pole work. If you have not read it, I recommend it. Perry makes some very good points in relation to system pressure between the pump and brush head. The article also explores the effect of pressure on your hose line.

So is this just more of the same I hear you ask. In short no. What I would like to do is pick up the baton so to speak continuing to expand on some of the points already made and introduce the pump control into the mix

I want to explore what creates the pressure and in doing so I will touch on some of the following points:

  • Pump Manufacture EG a Flojet pump generates different pressure to a Shurflo
  • Age of the pump-efficiency of the pump motor and quality of the brushes in the motor
  • Length of hose being used
  • How much hose is off the reel
  • Hose size
  • Expansion rates of the hose
  • Water Viscosity (cooler water flows slower) again impacting on pressure day to day
  • Flow rate set by the user
  • Size of the jets ( We recommend nothing smaller than 2mm )
  • Battery voltage and battery cells
  • Poor wiring or connections

Then lastly, but by no means least, the impact a controller will have together with reducing the system pressure could mean you work more efficiently.

First the easy bit the control will operate

  1. With any 12V DC 7amp pump in the market
  2. It will run with 8 - 6 and 4mm hose and micro bore
  3. It will run with 12V and 9V DC batteries
  4. The PSI of pumps range between 40PSI and 150PSI
  5. The control can be calibrated to a range of the above easily
  6. Once Calibrated the Auto adjust feature takes care of what pressure is required and when.

The controls are engineered to be a flexible as possible as there are so many variables.

There are a number of pumps on the market Sureflo, Flowjet, Chen to name a few. More and more pump manufacturers are recognising the size and scope of the pure water cleaning market and are producing better and more efficient pumps. Some pumps are more efficient than others in their use of current. Less current drawn the longer each battery charge will last.

What then are the drivers for creating pressure in your system?

  • The pump
  • Restrictions, for example, manual taps, jets. Dirt. Twists or kinks in the hose.
  • Hose expansion rate
  • Height of the pole

One of the main contributors to system pressure is the pump. Simply put the faster the pump turns the higher the pressure. An older pump may be less efficient than a new one particularly if run with no controller. The faster the pump runs the higher the wear on the bearings and the hotter the pump becomes. This can mean the pump loses efficiency as it gets hotter, the current is used to generate heat as opposed to pushing water. As the pump tries to work harder to compensate it draws more current generating even more heat. This in turn effects the pressure in the system reducing it and in turn reducing the flow. As the pump gets older this cycle is magnified.

As a general rule, the newer the pump the more efficient. However, keeping the pump motor brushes clean and in good condition, plus ensuring the pre-filter is kept clear your pump life can be extended.

Running the pump at maximum is likely to shorten its life as the motor is continually operating under very high inductive loads (stored energy). Ideally the system need to have sufficient capacity to cover a range of jobs. Simply running a pump flat out is just as likely to reduce the flow due to hose wall friction, plus create high pressure as described above. Using a smaller diameter hose may simply exasperate the issue.

Restrictions in your system create pressure as they each in turn slow the water and interrupt the natural flow created by the pump. Manual taps angle adapters kinks and twists in the hose will all increase the pressure in your system. Strangely however, this increased pressure does not mean the water will flow faster as friction between the restriction and water slows the water.

The Length of hose will also have an effect EG 100M against 60M simply put the water has less distance to travel so less pressure is required. The more hose that is run out the more expansion in the hose wall so the higher the pressure required to pump the water at the same flow reducing the flow.

A larger bore hose EG 8mm may generate lower pressure yet give more velocity as there is more water in the hose. However Hose wall stiffness will again effect the amount of pressure the softer the hose wall the greater the expansion capacity the slower the system is to pressure and water may flow at a lower pressure when compared to a hose with a stiffer wall construction.

A stiffer hose wall builds the pressure faster which can result in higher pressure in the system. Where a pump control is being used the pressure will ultimately be the same in both scenarios, the difference is in how fast the system pressures up to achieve the required flow.

Different manufacturers of hose will have different expansion characteristics, as previously mentioned this expansion rate will directly affect how quickly the system will pressure. We know that ambient air temperature has an effect on these expansion characteristics the colder the temperature the stiffer the hose wall and the faster pressure will build. Also colder temps effect water viscosity colder water flows slower (See below) This can mean that the same set up will be effected dependent on temperature on a day to day and in some cases hour to hour basis.

Next we consider flow rates the user prefers. The lower the flow rate the lower the pressure. However even here any of the above factors will also impact on hydraulic pressure in a system. The ability to adjust the flow rate to suit the job at hand is key. A question to be asked may be Do I need maximum flow at all times?

High flow in particular in UK and EU systems is likely to lead to very high pressure build up in the hose lines as the jets restrict the water. This in turn creates a fast powerful jet creating lots of splash back a cause of spotting. Looking to reduce the pressure or possibly use fan jets to give a higher water volume delivered to the glass will help you find a more efficient system

A controller can help the user manage and adjust water flow as required ensuring the correct amount of water is hitting the glass at any time. Looking to reduce flow will also reduce the pressure in your system. The controller is able to auto adjust the pump speed to ensure the desired flow rate is maintained.

So Just how much pressure builds up in a system?

To answer this question I set up a test using a Flojet 100psi 12V pump capable of generating 1.4 Gallons (5.3 LPM) the set up included a 25 foot pole and a 100M hose on a reel. As much as possible I replicated the flow through the system both with and without a V11 controller.

Please see table below

flow 20 40 60 80 99 Full
NC Pressure na na na na na 100psi
NC PS activation na na na na na 115psi
NC prior to PS na na na na na 120psi
NC Current na na na na na 7.5amps
C Pressure 20psi 35psi 40psi 70 psi 78 psi na
C Pressure at DE 42psi 45psi 62 psi 80 psi 98 psi na
C Current 0.97amps 1.7 amps 2.4 amps 4.14 amps 5.3 amps na
C Current at DE 1.15amps 2amps 3.15amps


6amps na
Calibration 32            

KEY: NC = no control. C = with control. PS = pressure switch. DE = dead end

Flow 20 40 60 80 99 Full
NC Pressure na na na na na 110psi
NC PS activation na na na na na 115psi
NC Prior to PS na na na na na 120psi
NC Current na na na na na 7.5 amps
C Pressure 28 psi 44 psi 50 psi 78 psi 80psi na
C Pressure at DE 63 psi 80 psi 95 psi 104 psi 104 psi na
C Current 1.06 amps 1.9 amps 2.7 amps 4.2amps 5.8amps na
C Cureent at DE 1.7 amps 2.7 amps 4.6 amps 5.3amps 6.2amps na
Calibration set at 60            

KEY: NC = no control. C = with control. PS = pressure switch. DE = dead end


For the test a Flojet 100PSI pump generating 5.3 LPM with a maximum current rating of 8amps was used. With a 100m of hose on a reel with water returned to the tank.
High lighted in Red is the pressure and amount of current drawn by the pump when connected directly to a battery. Remember as the pressure switch activates and stops the pump the conductive load across the switch is 7.5amps. As the pump stops this load does just disappear it arcs across the switch.

Add to this the high pressure in the whole system up to a 120PSI placing a huge strain on all the connectors and hose lines

Highlighted in green shows the control well within its working range, used in this range the control will give long service. Blue shows the upper ranges for continuous use with Black used for short periods only perhaps to rinse,

Clearly we can see the huge difference for example at a flow rate of 60 with the control calibration at 60 working pressure is a whopping 60 psi Lower - Current draw is 5 amps an hour less. When combined with different size jets this will still give the user 3 – 4 LPM delivered to the window.

Of Note even at a calibration of 60 with flow at 99 the pump is stopped at 104PSI while still high this is 16PSI lower than compared to no control. While appearing insignificant these could be all the difference required to split a hose burst a connector or burn out you pressure switch. When added to the down time while replacing or repairing the system the costs are anything but insignificant.

2mm jets are common in Europe where water management dictates pressurising the water to create a fine jet of water, this also has the effect of reducing the amount of water used per clean.
Jet size will have a big impact on the system pressure as we are effectively creating a restriction in the water line. We recommend nothing smaller than 2mm jets in the brush. Anything smaller causes very fast pressure build up and the control will assume water flow has stopped and shut down the pump. DE (dead end) will be displayed. These restrictions do mean that PSI in the system can be changedat the brush head by using different sized jets, and in fact mean a lower value PSI pump could be used in some cases.

The height the pole is working at will also have a bearing on pressure. The higher the pole is extended the greater the effect of gravity has on stopping the water flowing to the brush head.

So just how much pressure do you need to clean windows? (water fed image)

As a general rule 5PSI of pressure will push water up 10 feet or one story. However we need to take into account how much pressure is lost during hose wall expansion together with how much hose is run out and the efficiency of the pump. This lost pressure may mean in some cases more than 5PSI is required per story. The Jets will add pressure back into the system as outlined above. As most cleaners use 100PSI pumps these should provide more than enough pressure for the majority of WFP systems.

What is clear is that the higher you work the more pressure in your system must be increased this can be achieved by adjusting the speed of the pump ( a controller will do this automatically) or opening a tap further.

Now the good news

A very efficient way to achieve this is with an electronic flow controller. The control is a very versatile flexible piece of kit and is engineered to operate with a very wide range of systems, hose, pumps jets and poles. Once the control is calibrated to the system it will manage it knows the minimum and maximum working pressure of the system. As the pole is extended and higher pressure is required the controller auto adjusts the pump speed to ensure sufficient pressure to maintain the flow.

In Effect then the controller is doing all the work in maintaining the desired flow and correct pressure to maintain it. Leaving you to get on and Earn.

NOTE: If the control is unexpectedly dead ending the pump or the flow is pulsing this can be an indicator that the control has not been calibrated correctly. The following link shows how to auto calibrate the controller

What is Viscosity?

You will find many detailed technical explanations on line. For our purposes Viscosity is the thickness of a Liquid or liquid based product. Water has a low viscosity as it is thin and normally flows easily Oil in comparison has a high Viscosity it is thick and flows slowly.

The temperature will effect the viscosity of both water and Oil for example as they are heated the viscosity is lowered allowing the oil to circulate freely around your engine and lubricate it.

Water is effected by temperature in the same way in the summer months you may find that flow rates are higher than in winter due the fact the water is thinner and will flow faster.

More noticeable, is that in winter water viscosity changes as the cooler air temperature effectively makes the water thicker meaning the water will flow slower. Imagine the difference in pouring a cup of coffee against a Slush puppy which in effect is liquid ice.

The Viscosity of water in your system will effect the pressure as 1. The water is moving slower and 2. The hose walls will expand slower. Combined these two effects will make your system slower to pressure up in winter than in summer. Depending on how your system is set up together with the calibration and flow settings some may see no change or at least it is so slight not to be an issue.

Others may find a noticeable drop in water flow in the winter months caused by this change to the Viscosity (thickness of the water). The remedy is quick and easy – recalibrate the controller to take into account this slower water and the change in pressure dynamic.

Any blockage dirt - grit - air locks will have an effect on pressure. The system may take longer to pressure up than normal or you may find the pump pulses. Blocked jets will also mean that a pump is working very hard but generating little or poor water flow. It is important to remember to fit and clean the pre-filter on your pump regularly.

Battery condition and voltage available will also have an impact. A battery with low volts will struggle to get the pump to work properly which in turn will effect pressure.

Copper while being a reasonable conductor of current is also a resistor. It is not a 100% efficient conductor, This resistance factor means that some energy is lost, causing a drop in voltage available from the battery. Poor quality cable and connectors can make the volt drop worse - poor voltage can impact on system pressure as the pump is unable to draw sufficient current to operate properly.

A Battery with low volts available, worn brushes and even motor efficiency (for example an old pump is less efficient than a new one) can effect system pressure as will poor damaged or worn electrical connections.

Poor water flow could be a symptom of volt drop. Some controllers will give you Accurate at Battery voltage. Other controllers the voltage shown is measured at the controller not the battery. To check for volt drop check the controller display and then using a separate volt meter check the battery. I would expect to see some difference due the resistance effect of copper the difference may only be 0.1 of a volt and such a small drop would not be cause for concern. However if it is much higher for example 0.5V or more.

Note: Old wiring corroded connectors broken connectors will all have an impact on any volt drop down the cable, Also there may be a break in the cable worn or damaged insulation that will again cause a volt drop. In some cases, it may be worth replacing old or worn cables and connectors.

Note: We recommend for a single pump system that as a minimum a 75AH leisure battery is used. For two pump systems a minimum 110AH battery should be used. As the pump(s) draw current (amps) from the battery the volts are directly affected Ohms Law

Remember in General the each pump will draw between 3 and 5 amps an hour depending on how fast and efficient the pump is. As the amps available fall initially volts fall steadily however after continuous use the Volts will fall away sharply as shown below.

A pump controller added to your system will monitor pressure extending the life of your system as it is under less strain. It may also be that a smaller pump is required dependent on your work round a 60PSI may be more than sufficient.

System Pressure - Do we need to work at maximum pressure the whole time? (image 1)

Running the system at maximum places a very high strain on the pump motor, hose lines, connectors and pump pressure switch. A pump regulator greatly reduces the risk of the pump pressure switch burning out. A pump working at maximum pressure is under a high inductive load (stored energy). The user is relying on the pressure switch to stop the pump when the flow is stopped.

The pump pressure switch cuts in at maximum pressure with the motor under a high load (and high stored energy) thus causing arcing across the circuit which then burns out the pressure switch. Pump controls use PWM (pulse wave modulation) to slow the pump motor and reduce this high inductive load when the water flow and pump are stopped.

At maximum pressure you will have a jet of water up to 15 feet from the brush head, The water is bouncing back off the glass on to you and the ground and it is not cleaning the glass. A controller allows you to reduce this pressure to exactly that required.

So why calibrate the controller to a pump?

What we are doing is telling the control what the maximum pressure the system normally operates at. To get a good flow at the brush head the system is probably running between 40 - 70 PSI. So the control knows that the normal max level is 70 PSI. When a user stops the water flow the pump will attempt to push against the restriction increasing the pressure above 70 PSI the pump sees this sudden rise and stops the pump. This is what we refer to as DEAD END (DE).

During this DE (flow stopped period) the controller periodically retests the pressure at the pump. When the restriction is removed the pressure falls back below the 70PSI maximum and the controller restarts the pump at the preset flow. Hence the need to use auto calibration with the pole attached with some hose off the reel. For an efficient two pole system I would recommend two pumps and controls or the new Dual control.

The control is designed to stop the pump before the pump pressure switch activates where the water flow has been stopped. A pump pressure switch may activate at 110PSI give or take (based on 100 PSI pump) as described earlier running the pump to these high levels can cause problems.

In summery then there are many factors which will impact on the pressure in your system and ultimately the water flow and efficiency of your whole system. It is well worth spending time looking at how pressure effects your system. High pressure over long periods will increase the risk of system failures and lost productivity, meaning timely and costly repairs. A pump controller properly calibrated to your system not only manage and monitor your system it will aid your efficiency allowing you to earn more. Gaining good flow rates is not simply about pressure it is about having a well thought out system that allows flexible working practice to suit you and your round.

For most going to work is a means to an end we work to live. So consider, this is your system as efficient as it could be? If not a controller may be one step to a more efficient way of working along with considering the whole system. Your system represents a large investment in your business Information helps better understand how the system works plus the ability to ask questions of others and yourself on how and where you can work smarter not just harder.