Water Dynamics within Water Fed Pole systems
Water Dynamics and Hydraulic pressure in WFP
Many articles talk about back pressure - flow rates - water volume and delivering the right volume of water effciently. Just what does this all mean and can we find a balance to ensure the system works reliably time after time
This blog will delve into some of the detail and try make sense of it all.
What then are the drivers for creating pressure and flow in your system?
- Pump EG a Flojet may differ in pressure to Shurflo
- Age of the pump & efficiency
- Hose ID effects
- Expansion rates of the hose
- Water Viscosity what is it
- Flow rate/Volume
- Impact of brush jets
- Battery voltage and battery cells
- Poor wiring or connections
- Laminar V Turbulent flow
- Using a Pump controller
There are a number of pumps on the market Sureflo, Flowjet, Aquatec 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 to generate simply flow.
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 harder a pump runs the higher the wear on the bearings and the hotter the pump becomes. As the pump heats in order to maintain flow the oump draws higher current this is used to heat the motor rather than pushing water. As the pump gets older this cycle may be 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 will actually reduce flow. Using a smaller diameter hose may make the issue worse and cause the pump pressure switch to cycle on/off and interupt flow.
Restrictions impact on 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 effect the pressure in your system. Strangely however, high pressure does not mean water volume increases as friction between the restriction and water slows the water.
The Length of hose will also have an effect EG 100M against 60M as the water has less distance to travel 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.
A larger bore hose EG 8mm may generate lower pressure yet give more water volume 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.
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 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.
Lets look specifically at the water and hose. Once we know that the hose has a maximum capacity, for example 2.5LPM trying to force more water into the hose will reduce flow.
To answer why this happens, we need to look at three flow states
- Laminar (Smooth flow water all travels in the same direction at the same rate)
- Transitional (Less smooth becoming uneven)
- Turbulent (Chaotic Water travels in different directions all at once)
Laminar flow means the water is flowing smoothly with very little resistance. Think of the water as having layers what we are looking for is that each layer is moving smoothly over the one below, so in this way all the water is moving in the same direction ( another good example would be a multi lane road with all the traffic moving at the same speed in the same direction. In this way a Motorway/Free way can carry a large volume of traffic with no problem.
This is the most efficient state and will mean the pump is working only as hard as it needs to. There will be little to no strain on the pump motor, hose or connectors.
Transient flow means that the hose is reaching its maximum capacity and the hose wall is creating resistance to the water. Now rather than smooth layers of water all moving in one direction. The water flow begins to break up and the layers begin to cross over each other. Using the busy motorway/free way example from above imagine you are now approaching a junction with traffic joining and leaving. The traffic is now travelling at different speeds and people are changing lanes. This has the effect of slowing everybody down and the traffic bunches up. Its still moving but not as well as before.
Turbulent flow means that the hose capacity has been exceeded and the pump is now trying to force more water into the hose than it can take. Now the water flow is very uneven with layers of water becoming confused and moving in all directions at once, so the water flow becomes chaotic. Using our motorway example above imagine its rush hour and a truck has broken down in the middle lane. The resulting traffic slows to a crawl as drivers try get around the obstruction.
Why should this matter?
Once the movement of water becomes turbulent engery is lost as the wter moves in diferent directions with in the hose. Plus as the hose capacity is exceeded the amount of resistance created by the hose increases.
A 100psi 8 amp pump is common in water fed cleaning, typically the pump is capable of moving 5.2LPM (1.2 GPM) provided the outlet is not restricted. Once a hose is connected a restriction has now been introduced and flow will be limited by the capacity of the hose
Running a pump flat out straight from the battery does not increase the water flow or volume. Water volume and flow will be reduced. A hose has a maximum carrying capacity (flow rate) for example an 8mm ID hose this is 2.5LPM (0.6 gallon per minute) Having the pump produce more water at the outlet and into the hose will not increase flow through the hose or to the brush. This is because the water has become turbulent. All we actually have is the pump working very hard for no gain. The 8mm ID hose can still only carry 2.5LPM.
It makes no sense then to try push more than 2.5LPM into our 8mm hose. The effect of running the pump flat out simply means the pump draws high current and becomes hot, It also puts high strain on the pump motor, hoses and connectors.
It is about finding a balance that allows your whole system to operate efficiently, minimise break down and most importantly earn you money every day.
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 pressure build up in the hose lines as the jets restrict the water creates a fast powerful jet. This may cause lots of splash back pulling debris from th. surround a cause of spotting. Looking to reduce the pressure or possibly use fan jets to give a higher water volume delivered to the glass and give a curtain of water making rinsing easier. Rinse bars are becoming common and give the curtain effect. They also create slow moving hiher volumes of water.
A controller can help the user manage and adjust water flow as required ensuring the correct amount of water on 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
|NC PS activation||na||na||na||na||na||115psi|
|NC prior to PS||na||na||na||na||na||120psi|
|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||
KEY: NC = no control. C = with control. PS = pressure switch. DE = dead end
|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.8
Jet size will have a big impact on the system pressure as we are effectively creating a restriction in the water line. Very small pencil ID jets will increase the speed of the water but reduce the volume applied to the glass. Fast moving jets of water create splash back.
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 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 required 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 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 monitors pump current draw. 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 selected.
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 http://www.youtube.com/watch?v=9kKoskb7l7c&list=UL
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, worn pump 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 http://en.wikipedia.org/wiki/Ohm%27s_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 the pump and battery 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?
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.