A centrifugal pump converts input power to kinetic energy by accelerating liquid in a revolving device - an impeller. The most common is the volute pump - where fluid enters the pump through the eye of the impeller which rotates at high speed. The fluid accelerates radially outward from the pump chasing and a vacuum is created at the impellers eye that continuously draws more fluid into the pump. The energy from the pumps prime mover is transfered to kinetic energy according the Bernoulli Equation.
The energy transferred to the liquid corresponds to the velocity at the edge or vane tip of the impeller. The faster the impeller revolves or the bigger the impeller is, the higher will the velocity of the liquid energy transferred to the liquid be. This is described by the Affinity Laws. This maximum head is mainly determined by the outside diameter of the pump's impeller and the speed of the rotating shaft. The head will change as the capacity of the pump is altered. The kinetic energy of a liquid coming out of an impeller is obstructed by creating a resistance in the flow.
The first resistance is created by the pump casing which catches the liquid and slows it down. When the liquid slows down the kinetic energy is converted to pressure energy. A pump does not create pressure, it only creates flow. The gauge pressure is a measurement of the resistance to flow.
In fluids the term head is used to measure the kinetic energy which a pump creates. Head is a measurement of the height of the liquid column the pump could create from the kinetic energy the pump gives to the liquid. The pump's performance on any Newtonian fluid can always be described by using the term head.
The head is measured in either feet or meters and can be converted to common units for pressure - like psi, Pa or bar. The only difference between the fluids is the amount of power it takes to get the shaft to the proper rpm. The higher the specific gravity of the fluid the more power is required.
Note that the latter is not a constant pressure machine, since pressure is a function of head and density.Make FireRescue1 your homepage. Are first responders eligible for a stimulus check? There are two ways to calculate friction loss: the theoretical method or the fireground method — here's the fireground method. There are plenty of things that the pump operator must get done in the early stages of a fire, and none are more important than this. To determine this, the pump operator must first know the total gallons per minute flow, that is, the desired result on the working end of the hose.
The type of nozzle being used — smooth-bore, automatic nozzle or adjustable gallonage — will determine the gpm. Once the pump operator knows what the desired gpm is, then they must know what size hoses are being used, the lengths of the hoses and any appliances that are part of the hose layout, such as a gated wye.
Armed with that information, the pump operator can then calculate the friction loss, the remaining ingredient for getting the right mixture to their firefighting colleagues. Friction is the force resisting the relative motion of solid surfaces, fluid layers and material elements sliding against each other. Friction loss is the pressure loss due to the friction. In its fire service application, the friction is water sliding against the interior surfaces of the pump, any connected appliances — gated wyes, manifolds or a water thief — standpipes and fire hose.
In reality, understanding friction loss and its place in properly supplying hose lines and fire streams is not that daunting of a task.
The basic challenge for the pump operator is to develop the proper pump discharge pressure necessary to overcome the friction loss in a fireground set up to ensure that the firefighter on the nozzle will have the appropriate amount of water to suppress the fire. There are two ways to calculate friction loss: the theoretical method or the fireground method. Theoretical calculations are generally best used for pre-fire planning, developing specifications for pumping apparatus and calculating problems ahead of time, such as creating pump charts.
Theoretical calculations are typically not an efficient means of calculating friction loss on fire scenes. Many times, instructors teaching pump operations bring out the theoretical method, along with its equations, at the beginning of the training process. I was very fortunate at the beginning of my firefighting career to join a department where that was not the case.
My pump operator instructors focused early on developing my skills in using such tools as the hand method for calculating friction loss.Pump Head: Simple Explanation
They also emphasized memorizing the friction loss for the pre-connected hand lines and typical hose layouts that I would encounter as a pump operator. This is an extremely valuable tool for both learning and teaching what the friction loss is for various sizes of hose and various gpm flows. Below is one example of a hand method for calculating friction loss in various sizes of hose. For a 3-inch supply line flowing gpm, the friction loss per foot section would be 9 psi: 3 squared equals 9 psi.
Memorizing this much simpler than it sounds. All you must remember is the friction loss for each, 14, 24, 35 and 62, respectively. Those are the amounts of friction loss per feet of hose based on the gallonages above. Change the flow setting on the nozzle to gpm on the same foot line and the friction loss is 35, if you increase the hose length to feet, the friction loss becomes 62 psi.
To figure the required discharge pressure, add up all friction loss — in the hose and any appliances — plus the required nozzle pressure. Thus, for that apartment complex layout I mentioned earlier, the calculation would look like this:.
Do your homework about the different hose loads, appliances and nozzles used in your department and what each contributes to friction loss, that is, what are the friction loss points. A best practice employed by many skilled pump operators is creating a cheat sheet containing what those friction loss points look like. Source: University of Alaska, Fairbanks. The Physics of Fireground Hydraulics. April My fire service colleague with the Henrico County Va.Pump operators have one of the most critical jobs within the fire company.
They must be able to deliver the troops in a timely and safe manner and provide them with an adequate water flow to suppress the fire as fast as possible.
This involves securing a water supply sufficient enough to produce the required fire streams to get the job done, and to develop the required streams by means of a combination of hose evolutions and proper pump operations. A pump operator should understand the operation and capabilities of all appliances that have anything to do with the movement of water, such as:.
There are things that a pump operator needs to know in regards to physics when it comes to delivering water on the fire ground. Here is a list of things to know about moving water that will help the pump operator to have a better understanding of what is required of him.
Besides all of the above-mentioned items, the pump operator needs to develop the proper discharge pressure to provide the energy to move the water through the hose evolution and discharge it onto the fire. There are several things in a hose evolution that require pressure to move the proper amount of water.
Back in the olden days when buckets were used, the only energy required to move the water was in the form of human power in bucket brigades. There have been several methods used over the years to calculate the required discharge pressure, some worked well and others not so well.
I wonder how many people practice that these days. If water comes out the other end, the correct discharge pressure is being developed. I think you know these methods leave a lot to be desired. Probably one of the most common methods used for calculating the right discharge pressure is the use of fireground hydraulics.
This is a mathematical formula that is based on the size and length of the hose line, the amount of water being delivered GPMappliance friction loss, elevation gain or loss, building plumbing loss, and nozzle pressure. In other words dimensions.
Put the Pump Chart on the Pump Panel
A coefficient could then be used in the formula to apply it to other hose diameters. I know this formula works on paper with the help of a calculator, but is it practical and accurate? No and no. First off, hose has different characteristics than pipe. It is a proven fact that the same size hose at a given flow can have different friction loss characteristics from different manufacturers. The following statistics show just that.You may not of thought of some of these and they will help you design and trouble-shoot pump systems and select the proper pump.
Also there is information here that is hard to find elsewhere. You can also download these tips in pdf format. When the flow increases, the discharge pressure of the pump decreases, and when the flow decreases the discharge pressure increases ref.
Do not let a centrifugal pump operate for long periods of time at zero flow. In residential systems, the pressure switch shuts the pump down when the pressure is high which means there is low or no flow. Make sure your pump has a pressure gauge on the discharge side close to the outlet of the pump this will help you diagnose pump system problems. It is also useful to have a pressure gauge on the suction side, the difference in pressure is proportional to the total head.
The pressure gauge reading will have to be corrected for elevation since the reference plane for total head calculation is the suction flange of the pump. These web apps will help you calculate total head from pressure.
CENTRIFUGAL PUMP SYSTEM TUTORIAL
Most centrifugal pumps cannot run dry, ensure that the pump is always full of liquid. In residential systems, to ensure that the pump stays full of the liquid use a check valve also called a foot valve at the water source end of the suction line. Certain types of centrifugal pumps do not require a check valve as they can generate suction at the pump inlet to lift the fluid into the pump. These pumps are called jet pumps and are fabricated by many manufacturers Goulds being one of them.
Gate valves at the pump suction and discharge should be used as these offer no resistance to flow and can provide a tight shut-off. Butterfly valves are often used but they do provide some resistance and their presence in the flow stream can potentially be a source of hang-ups which would be critical at the suction.
They do close faster than gate valves but are not as leak proof. Always use an eccentric reducer at the pump suction when a pipe size transition is required.
Put the flat on top when the fluid is coming from below or straight see next Figure and the flat on the bottom when the fluid is coming from the top. This will avoid an air pocket at the pump suction and allow air to be evacuated. For deep wells feet a submersible multi-stage pump is required. They come in different sizes 4" and 6" and fit inside your bore hole pipe. Pumps with different ratings are available. If you need to control the flow, use a valve on the discharge side of the pump, never use a valve on the suction side for this purpose.
This is an excellent treatment of the types of control systems for a centrifugal pump by Walter Driedger. And also this article by the same author on how to control positive displacement pumps. For new systems that do not have a flow meter, install flanges that are designed for an orifice plate in a straight part of the pipe see next Figure and do not install the orifice plate.
In the future, whoever trouble-shoots the pump will have a way to measure flow without the owner having to incur major downtime or expense. Note: orifice plates are not suitable for slurries.
CENTRIFUGAL PUMP SYSTEMS TIPS
Avoid pockets or high point where air can accumulate in the discharge piping. An ideal pipe run is one where the piping gradually slopes up from the pump to the outlet. This will ensure that any air in the discharge side of the pump can be evacuated to the outlet.
Be aware of potential water hammer problems. This is particularly serious for large piping systems such as are installed in municipal water supply distribution systems.
These systems are characterized by long gradually upward sloping and then downward sloping pipes. This will avoid water hammer during the initial start and damage to the piping system.We have received several questions about how to read centrifugal pump curves, so we'll address the most common questions in this blog.
Pump curves help you select pumps for the specific needs of your application. Pump curves give you the information you need to determine a pump's ability to produce flow under the conditions that affect pump performance. Curves help you choose the right pump based on the application variables such as head water pressure and flow the volume of liquid you have to move in a given time period. The curve will show you if the pump you have selected will perform in that application.
Pump curves are useful because they show pump performance metrics based on head pressure produced by the pump and water-flow through the pump. Flow rates depend on pump speed, impeller diameter, and head. Head is the height to which a pump can raise water straight up. Water creates pressure or resistance, at predictable rates, so we can calculate head as the differential pressure that a pump has to overcome in order to raise the water. Common units are feet of head and pounds per square inch.
As Figure 1 illustrates, every 2. Flow is the volume of water a pump can move at a given pressure. Flow is indicated on the horizontal axis in units like gallons per minute, or gallons per hour, as shown in Figure 2. While pump curves help you select the right pump for the job, you first have to know the total dynamic head for the application. Total Dynamic Head TDH is the amount of head or pressure on the suction side of the pump also called static liftplus the total of 1 height that a fluid is to be pumped plus 2 friction loss caused by internal pipe roughness or corrosion.
Learn more about centrifugal pumps and key calculations. Let's say you want to know the flow rate you can achieve from the pump in Figure 3 at 60 Hz when the design pressure is 80 PSI. In this case, the curve shows that the pump can achieve a flow rate of gallons per hour at 80 PSI of discharge pressure. Because some pumps operate across a range of horsepower, their curves will include additional information.
Figure 4, for example, features a pump that can operate from 2 to 10 horsepower depending on desired performance.
Impeller size is another variable for meeting performance requirements. The curve above shows impeller trim sizes, at the right end of each curve, ranging from a minimum of 4. Reducing impeller size enables you to limit the pump to specific performance requirements.
The curve above shows maximum pump performance with a full-trim impeller, minimum pump performance with a minimum-trim impeller, and performance delivered by the design-trim impeller, or the impeller trim closest to the design condition.Total head and flow are the main criteria that are used to compare one pump with another or to select a centrifugal pump for an application.
Total head is related to the discharge pressure of the pump. Why can't we just use discharge pressure? Pressure is a familiar concept, we are familiar with it in our daily lives. For example, fire extinguishers are pressurized at 60 psig kPawe put 35 psig kPa air pressure in our bicycle and car tires.
Developing Pump Discharge Pressures
For good reasons, pump manufacturers do not use discharge pressure as a criteria for pump selection. One of the reasons is that they do not know how you will use the pump. They do not know what flow rate you require and the flow rate of a centrifugal pump is not fixed. The discharge pressure depends on the pressure available on the suction side of the pump. If the source of water for the pump is below or above the pump suction, for the same flow rate you will get a different discharge pressure.
Therefore to eliminate this problem, it is preferable to use the difference in pressure between the inlet and outlet of the pump.
The manufacturers have taken this a step further, the amount of pressure that a pump can produce will depend on the density of the fluid, for a salt water solution which is denser than pure water, the pressure will be higher for the same flow rate. Once again, the manufacturer doesn't know what type of fluid is in your system, so that a criteria that does not depend on density is very useful.
You can measure the discharge head by attaching a tube to the discharge side of the pump and measuring the height of the liquid in the tube with respect to the suction of the pump. The tube will have to be quite high for a typical domestic pump.
If the discharge pressure is 40 psi the tube would have to be 92 feet high. This is not a practical method but it helps explain how head relates to total head and how head relates to pressure.
You do the same to measure the suction head. The difference between the two is the total head of the pump. The fluid in the measuring tube of the discharge or suction side of the pump will rise to the same height for all fluids regardless of the density.
This is a rather astonishing statement, here's why. The pump produces pressure and the difference in pressure across the pump is the amount of pressure energy available to the system. If the fluid is dense, such as a salt solution for example, more pressure will be produced at the pump discharge than if the fluid were pure water. Compare two tanks with the same cylindrical shape, the same volume and liquid level, the tank with the denser fluid will have a higher pressure at the bottom.
But the static head of the fluid surface with respect to the bottom is the same. Total head behaves the same way as static head, even if the fluid is denser the total head as compared to a less dense fluid such as pure water will be the same. This is a surprising fact, see this experiment on video that shows this idea in action. Total head is the height that the liquid is raised to at the discharge side of the pump less the height that it is raised to at the suction side see Figure Why less the height at the suction side?
Because we want the energy contribution of the pump only and not the energy that is supplied to it.Make FireRescue1 your homepage. Are first responders eligible for a stimulus check? If you are the assigned apparatus operator for your department and have your hydraulic pump chart memorized, this article is not for you. For the rest of us who struggled not to fall asleep in high school algebra, here is your scenario.
Its 3 a. Your unit's assignment is to protect exposures on multiple sides of the fire building. As soon as your apparatus is positioned and a hydrant is secured, lines are being deployed in multiple directions. Your two foot preconnected Speedlays, which are connected to the number one and two Speedlay outlets, are being deployed to protect some nearby homes.
A Rapid Attack Monitor R. The line is attached to the number four driver's side discharge. A "bundle" line consisting of two foot 2-inch hose lines with 1-inch smoothbore tips have been stretched to the Bravo side of the warehouse. The two lines are connected by a wye appliance to feet of 3-inch line, which is attached to the number three 3-inch outlet on the passenger side of the apparatus.
So what's the solution for those firefighters who, like me, can't keep all those numbers straight? The first step is to have an easy to use and readily available hydraulic pump chart, as seen above right. However, let's be honest — even departments that keep up-to-date charts on every apparatus rarely use them, and when they do, it's normally one or two numbers that are used ninety percent of the time.
A quick answer to the problem of ensuring your pump operators are using the correct discharge pressures is to place the most commonly used parts of the hydraulic pump chart on the pump panel itself. A label maker found in most office supply stores is an inexpensive solution to placing information on the pump panel, as seen below. Most manufacturers make a laminated label that is designed for outdoor use.
Give the pump panel a more professional look by using clear labels and placing them on the same reflective material used for apparatus striping:. Place the discharge pressures that are used ninety percent of the time near the discharge gauges associated with those pressures and the other ten percent, the pump operator will need to reference from the pump chart.
The numbers that should be placed on the panel are determined by the individual department's hose and nozzle setups. The first number should be the ideal gpm flow for the nozzle. If this is the nozzle carried on a preconnected line, the first number should show the required discharge pressure to flow gpm.
The second number should be a balance between the maximum gpm flow that two firefighters can handle and an acceptably performing water stream. See the image below:. With a two-pressure set up, instead of multiple requests to increase pressure coming from the nozzle team, one radio transmission allows the team to ask for the maximum amount of water they can handle.
Another common problem many apparatus operators encounter is trying to remember which discharge a hose line is attached to. Was it the 1 Discharge, the 1 Speedlay, or the 1 Crosslay that needs to be charged? NFPA states that all discharges be color coded and labeled to correspond with the appropriate discharge gauge on the pump panel, but does not specify what type of markings are required.
Many apparatus manufacturers use small colored labels glued above the individual discharges and gauges to meet the standard, as seen in the following photo. Older apparatus often are found to be missing the labels, or they have faded due to exposure. A quick and inexpensive solution to solve this problem is colored electrical tape.
Studies have also shown that individuals under stress can more easily remember a color than a number. Wrap the tape around the discharge outlet and the pump operator does not even need to get close to the outlet to determine which discharge the hoseline is attached to:. Finally, many apparatus operators find it difficult to determine the size of the tip when looking up at an apparatus-mounted deck gun, equipped with a set of smoothbore stacked tips.
By combining the label maker and electrical tape, a quick reference guide can be placed on the pump panel that correlates with the deck gun tip sizes. Wrap colored tape around each section of the stacked tips. Use the tape and label maker to create a color-coded chart identifying the discharge pressures needed to achieve the standard 80 psi nozzle pressure for a smoothbore master streams. The chart will give the pump operator an easy to use visual guide that allows them to flow between and gallons per minute on most apparatus.