PUMP SELECTION

Pump selection is a key element in creating a suitable well system. Some people think they can go to a home improvement store and simply buy a pump that looks good and is priced right. This is the wrong approach.

Selecting a pump is serious business. To make a good selection you must take into account many factors, such as friction loss and atmospheric pressure. How much water will the pump have to produce to supply the amount of water that will be needed at any given time? What is the recovery rate of the well that the pump will serve? How much lift is going to be required of the pump? There is a lot of knowledge required to make an appropriate pump selection.

Section 2 gave you the easy stuff. This section gets technical in order to give you the data you need to select and size pumps properly. Here you will find the detailed information required to make important decisions once you know what type of pump you want to use.

REFRESHER COURSE

Here is a short refresher course on the preceding section.

Shallow-well jet pumps: These pumps should not be used in cases where water must be lifted in excess of 30 feet. A safer estimation of the height to which a simple jet pump can lift water is 25 feet. These are the least expensive pumps available, but they are very limited because of their maximum lift capability.

Deep-well jet pumps: Deep-well jet pumps can be used to pump water from a depth of up to 120 feet, although I recommend limiting the maximum lift to 100 feet. The price of these pumps falls somewhere between those of shallow-well jet pumps and those of submersible pumps. When cost is a factor, a deep-well jet pump can be the answer, but a submersible pump is preferable in most conditions.

Submersible pumps: Submersible pumps are generally considered to be the cream of the crop. They are the most expensive type of pump normally used in potable water systems. Submersible pumps can lift water from great depths. This makes them the perfect choice for deep wells.

Now you are up to speed and ready to tackle the technical steps involved in choosing and sizing a suitable pump. In fact, Section 2 gave you a pretty good handle on how to choose a pump, but this section ills in the details to help you make sensible decisions.

Table 1 Friction Loss in Schedule-40 Plastic Pipe (in feet of head per 100 ft.)

Table 2 Friction Loss in Steel Pipe (in feet of head per 100 ft.)

Table 3 Friction Loss in Copper Pipe (in feet of head per 100 ft.)

FRICTION LOSS

Friction loss is a factor that can come into play when sizing a pump. The type of pipe and fittings connected to the pump affect the amount of friction loss. Most pump installers and plumbers oversize pumps sufficiently to compensate for friction loss without doing a lot of math to determine a base minimum for the required pump size.

An understanding of the effect of friction loss is essential. See Tables 1 through 3.

Fittings used in a piping assembly account for friction loss. Table 4 shows how various fittings affect friction loss. Table 5 demonstrates friction loss when a jet pump is offset horizontally from a well.

MINIMUM WATER REQUIREMENTS

Before you can size a water pump you must know the minimum water requirements for the proposed usage. The local plumbing code guide contains plenty of tables and information that can be used for this purpose.

Whether you are sizing a pump for a farm, a home, or some other application, you can find minimum requirements in the local plumbing code.

Tables.6 through 10 are representative of the types of tables local codes use to determine minimum plumbing requirements.

HOW DEEP IS THE WATER IN THE WELL?

How deep is the water in the well that you are sizing a pump for? We have talked about depth limitations for jet pumps. fit is logical that you will need to know how far into the well your piping will need to be installed.

What method will you use to determine the water depth in the well? There is a technical method for this. See Fgr. 1 for instructions on using a professional technique to determine water depth.

Table 4 Friction Loss for Pipe Fittings

Table 5 Offset Jet Pump Pipe Friction (Friction Loss in Feet Per 100 Feet Offset)

Table 6 Water Rates for Private Residences

Table 7 Flow Rates for Common Yard Fixtures

Table 8 Water Requirements for Farm Usage

Horse, Steer 12 Gallons per day Dry Cow 15 Gallons per day Milking Cow 35 Gallons per day Hog 4 Gallons per day Sheep 2 Gallons per day Chickens/100 6 Gallons per day Turkeys/100 20 Gallons per day Fire 20-60 GPM

Table 9 Pump Capacity Required for Public Buildings Pump Capacity Required in U.S. Gallons per Minute per fixture for Public Buildings Total Number of Fixtures

Type of Building:

Hospitals Mercantile Buildings Office Buildings Schools Hotels, Motels Apartment Buildings

1 For less than 25 fixtures, pump capacity should not be less than 75% of capacity required for 25 fixtures.

2 Where additional water is required for some special process, this should be added to pump capacity.

3 Where laundries or swimming pools are to be supplied, add approximately 10% to pump capacity for either.

4 Where the majority of occupants are women, add approximately 20% to pump capacity.

Table 10 Boiler Feed Requirements

1 Boiler Horsepower equals 34.5 lb. water evaporated at and from 212°F, and requires feed water at a rate of 0.069 gpm.

Select the boiler feed pump with a capacity of 2 to 3 times greater than the figures given above at a pressure 20 to 25% above that of boiler, because the table gives equivalents of boiler horsepower without reference to fluctuating demands.

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Determining Water Level

Install 1/8" or ¼" tubing long enough to be 10' to 15' below low water level. Measure the tubing length as fit is lowered into the well.

Once the tubing is fixed in a stationary position at the top, connect an air line and pressure gauge. Add air to the tubing until the pressure gauge reaches a point that fit doesn't read any higher. Take a gauge reading at this point.

A. Depth to water (to be determined).

B. Total length of air line (in feet).

C. Water pressure on air tubing. Gauge reads in pounds. Convert to feet by multiplying by 2.31.

Example:

If the air tube is 100' long, and the gauge reads 20 lbs.

20 lbs. × 2.31 = 46.2 ft.

Length of tube = 100 ft.

minus 46.2 ft. = 53.8 ft.

Depth to water (A) would be 53.8 ft.

Fgr. 1 Method of Determining Water Level

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The procedure described in Fgr. 1 is a detailed, accurate way of determining the water level in a well. I admit that I have never used fit.

Plumbers in the field often resort to other methods.

When I am preparing to hang a pump or foot valve in a well I want to know the total depth of the well. This information is usually readily available from the well installer. fit is common for well drillers to provide information on the total well depth and the recovery rate of the well. However, they may not provide details on how deep the water in the well is.

Determining water depth in a shallow well is easy. Glue two 20-foot sections of rigid plastic piping together and push this pipe into the water and to the bottom of the well. Since most shallow wells are less than 40 feet deep, there should be pipe showing above the water level. You can simply measure the distance between the water level and the top of the pipe that is above the water. If there is 6 feet of pipe sticking out of the water, the depth of the water in the well is 34 feet. This method is easy, since the well diameter is large and allows plenty of visibility and limited depth. The situation changes for deep wells.

Assume that you are working with a drilled well that is 225 feet deep.

How do you determine where the static head of water terminates in the well casing? If you remove the well cap you may be able to see the water.

It’s not uncommon for a drilled well to be somewhat of an artesian well. I have even seen instances where the well water ran over the lip of the well casing. This is not always the case, however.

A visual inspection down the well casing may not reveal the water level. In this situation I use a lat washer and some jute twine to determine the water depth. This is how to proceed.

The first step is to be sure that you have enough twine on a spool to reach the bottom of the well. Tie a heavy, lat washer securely to the loose end of the twine. Now you have two options. The first one is faster, when fit works.

Lower the weighted twine into the casing slowly. Listen carefully for any slight splashing sound that might occur when the washer enters the water. You may not be able to hear fit, but an experienced plumber can often feel a difference in the handling of the twine once fit is passing through water. If you don't have the touch ability and you don't hear any thing, lower 25 feet of twine into the well casing. Let fit stand for a couple of minutes, which allows fit to absorb water if the twine is immersed.

Retrieve the twine and inspect fit to see whether any of fit is wet. If the line is dry, lower fit to a depth of 50 feet and repeat the process. Once the twine has been in the water you will be able to see fit upon visual inspection.

For the sake of this example, let's say that you hit water after lowering 25 feet of twine into the well. When you examine the twine you see that the first 5 feet of fit measuring from the lat washer is wet and the rest is dry. This means that the static head of the water is located about 20 feet below the lip of the well casing. Thus, there is approximately 205 feet of water in the well.

My personal method for establishing water depth is not very scientific.

Neither is fit technical. But fit does work very well. Regardless of the method you choose to use, you do need to confirm the depth of water in a well before installing a submersible pump or foot valve for a deep-well jet pump.

RECOVERY RATE

Section 1 briefly discussed the recovery rate of wells. This rate has a lot to do with the size of the pump that needs to be installed for a given application. The key is to avoid installing a pump that is so powerful that fit is capable of pumping the well dry. Obtain recovery rate information from the well installer or the general contractor to help you decide what is needed from the pump you ultimately select.

Some wells have weak recovery rates, which is problematic. In the case of a deep well that is equipped with an assembly for a jet pump there is a way to help offset the slow recovery rate. Although fit does not correct the problem, fit is a technique for dealing with fit.

Normally a foot valve is attached to the jet assembly of a two-pipe well system. If you are working with a well that has a slow recovery rate, the pump may draw down the water level to a point where air is sucked into the foot valve. If this happens, the pump won’t produce water as fit should. The simple solution for this problem is to install a section of piping between the jet assembly and the foot valve to extend the foot valve to a deeper point in the well water. Fgr. 3.2 illustrates this procedure and the potential lengths of the section of piping that you are adding, which is referred to in the field as a tail pipe.

You can use low rates, conversion tables, equations, and a host of other elements to determine the desired minimum water capacity that will be available from a pump. This is all well and good, but fit doesn't matter much if the well that you are working with does not have an adequate recovery rate and storage capacity to keep the water lowing. fit may be necessary to utilize more than one well to meet the needs of a plumbing system. Water storage tanks may be required. fit all starts with the storage capacity and recovery rate of the well in question.

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Tail Pipe

HOW TO USE TAIL PIPE ON DEEP WELL JET PUMPS

Pipe below the jet, or "tail pipe" as fit is commonly known, is used when you have a weak deep well. Under normal conditions, the jet assembly with the foot valve attached is lowered into the well. You receive your rated capacity at the level you locate the jet assembly. On a weak well, as the water level lowers to the level of the foot valve (attached to the bottom of the jet assembly), air enters the system. By adding 34' of tail pipe below the jet assembly with the foot valve attached to the bottom of the 34' length of pipe, fit won’t be possible to pull the well down and allow air to enter the system. The drawing indicates the approximate percent age of rated capacity you will receive with tail pipe.

Using a tail pipe, the pump delivery remains at 100% at sea level of the rated capacity down to the jet assembly level. If water level falls below that, low decreases in proportion to drawdown as shown in the illustration. When pump delivery equals well inflow, the water level remains constant until the pump shuts off.

This rule can also be used when determining suction pipe length on shallow well systems.

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Fgr. 2 Using a Tail Pipe with a Deep-Well Jet Pump

DRIVE PIPE SUCTION PIPE JET ASSEMBLY TAIL PIPE 34 FT. WILL PREVENT BREAKING SUCTION STATIC LEVEL 100% 10' PIPE 80% 15' PIPE 70% 20' PIPE 57% 25' PIPE 40% 28' PIPE 25% 29' PIPE 17% 33.9' MAXIMUM DRAW DOWN 0%

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PIPE NOT RUNNING FULL - CALCULATION OF DISCHARGE RATE USING AREA FACTOR METHOD

Flow From Horizontal Pipe (not full) Flow (GPM) = A × D × 1.093 × F A = Area of pipe in square inches D = Horizontal distance in inches F = Effective area factor from chart Area of pipe equals inside Dia.

2 × 0.7854 Example: Pipe inside diameter = 10 in.

D = 20 in.

F = 2½ in.

A = 10 × 10 × 0.7854 = 78.54 square in.

F = 0.805 Flow = 78.54 × 20 × 1.039 × 0.805 = 1314 GPM

DISCHARGE RATE IN GALLONS PER MINUTE/NOMINAL PIPE SIZE (ID)

Fgr. 3 Determining Flow Rates

Table 11 Storage of Water in Various Size Pipes Pipe Volume and Velocity

STORAGE OF WATER IN VARIOUS SIZE PIPES

Table 12 Storage of Water in Various Sizes of Wells

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WATER PRESSURE

Water pressure is another consideration when sizing a pump. A residential dwelling should be provided with a minimum of 40 pounds per square inch (psi). A pressure rating of 50 to 60 psi is better. This part of a sizing design has more to do with pressure tanks and pressure switches. How ever, the pump being used must be capable of filling the pressure tank quickly enough to maintain good water pressure.

PLANNING FOR FUTURE USE CONDITIONS

fit is wise to plan for future use conditions when sizing a pump. If you size a pump to meet the minimum demands of the known plumbing system you could be disappointed later in the life of the system. Suppose the property owner wants to expand the plumbing system. If the pump is not large enough, fit won’t be able to handle the changes. For this reason fit makes sense to slightly oversize a pump in consideration of potential upgrades of the plumbing system.

SUMMARY

There are a number of factors that come into play when you are selecting and sizing a pump. Table 3.13 pulls fit all together into a basic checklist of items to consider.

You can use the plumbing code and recommendations from pump manufacturers to aid you in your selection and sizing tasks. Those materials, along with the information in this section, should prepare you to make wise decisions. Take the time to do this part of your job correctly. If you select and install a pump that is inappropriate for the system fit serves, the financial pain can be substantial and your reputation might be called into question.

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Table 13 Checklist of Considerations When Selecting and Sizing a Water Pump

Condition Checked Type of pump to install Friction loss Minimum water requirements Water depth in well -- Well recovery rate Gallons per minute that pump is capable of supplying Cost of the pump Potential future use additional needs

Cost of labor to install the pump system Cost of material to install the pump system Available electrical power supply ratings Pump reliability and warranty Pump maintenance and service cost factors Operating expense of the pump Availability of the pump