Explanation of Two Line Jet Pumps & Drinking Water Wells InspectAPedia® -
Explanation of deep-well Two Line Jet Pumps & Drinking Water Wells, Well Problems & Repair Advice
What are the components of a two line jet pump water supply system?
What types of wells use a two-line jet pump for water delivery. From what depth can a two line jet pump deliver water?
Types of wells and water supply systems and what to watch out for with each
Well pump & water tank diagnosis & repair procedures
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This article describes the components of a two-line jet pump water system, what the components look like, and what they do. This article series describes various types of drinking water sources like wells, cisterns, dug wells, drilled wells, artesian wells and
well and water pump equipment. We provide advice about what to do when things go wrong.
What are the Components of a Well with a Two Line Jet Pump?
Refer to the illustration at left, courtesy of Carson Dunlop and also to our rough sketch provided below to see the components providing well water to a building served by a two-line jet pump located apart from the well.
In our drawing the two line jet pump which draws water from the well and the water pressure tank are shown located separately from
the well itself, and the well and its casing are shown located inside of a well pit.
Well pits such as the one we've drawn are used especially in climates exposed to freezing weather, as a way to get
access to the well casing and well piping and to route well piping out of the well through the top of the well casing and on to
the building while protecting it from freezing.
In addition to showing a well pit in this sketch, we discuss and illustrate well pits a bit more
at Well Pits
How a Two-Line Jet Pump Works to Get Water Out of the Well
A two line jet pump refers to the observation that two pipes are connected between the jet pump and the well.
In our photo at left you can see the two black plastic lines leaving the front of the water pump.
A two line jet pump draws water out of the well by magic: it forces water away from the pump and into the bottom of the
well through one of the pipes (usually the smaller diameter pipe).
At the bottom of the well water from the jet pump
is forced through a venturi device (a sort of funnel shaped opening) and then back upwards into the larger diameter pipe.
Water flowing through the venturi device at the bottom of the well piping draws still additional water out of the well and into
the larger diameter pipe that flows back to the building.
The requirement to have some water to send down to the well in order to bring a larger quantity of water back is why a two line jet pump can't provide any water or water pressure in a building if it loses its prime. See WELL PUMP PRIMING PROCEDURE if you need to re-prime your jet pump.
In our sketch above see the two arrows showing water entering the bottom of the piping.
The following list and definition of two-line deep well jet pump and water well parts and terms is
organized from the top of the drawing towards its bottom and uses names that correspond to those shown in our ugly sketch above.
A pair of well pipes leave the well casing through a water-tight cap on top of the casing and
are connected to the appropriate fittings on the two line jet pump which is (probably) located in the building it
serves.
The well casing top in this example is located inside of a well pit but it
could be simply buried in the soil. It is particularly important that the well cap on the casing be water tight
since otherwise unsanitary surface water and
debris can enter the well casing. Many well caps are not water tight, which is why modern drilled well casings extend above ground level.
Compression Seal Well Cap is a special well cap with openings to permit passage of the two water lines (and maybe an air vent tube)
out of the well to above ground.
A compression seal well cap consists of steel top and bottom plates which "sandwich" rubber fittings which surround
the water piping. As the two plates are bolted together they squeeze the rubber "sandwich" gaskets causing them to expand and seal both around
the water piping and inside the diameter of the well casing.
A "two-line" jet pump is shown outside of the well, either inside of the building or perhaps in a well pit or well house. "Two line" refers
to the fact that two water pipes connect the pump to the well. Since the lift capacity of a two-line jet pump is not
limited to the shallow-well depth of 27' chances are that where you find a two line jet pump installed
it is drawing from a deep water well. Our sketch shows the pump connected to a water pressure tank which in turn supplies water to the
building. The pressure tank is usually located very close to the jet pump but it could be elsewhere.
Well Jet and Well Piping Foot Valve is a venturi device through which the two line jet pump sends water to collect and
bring still more water back into the building. You can see Carson Dunlop's sketch of a foot valve here and also at the end of this list.
Well Jet & Foot Valve Clearance from Well Bottom: (not shown) means that the well piping, bottom venturi, and foot valve are inserted
into the well some distance from the very bottom of
the well (inches to a few feet). We need this clearance to reduce the tendency of the well pump to pick up mud and debris from the bottom of the well.
Static head (not shown in this sketch) is the height of the column of water inside of the well between the bottom of the foot valve and the
top of the water when the well is at rest. We discuss "static head" and well recovery rates in detail at How Much Water is In the Well?
What is a Foot Valve used in a well and what goes wrong with foot valves?
If you keep losing prime at the water pump where a two-line jet pump is installed, it's probable that a check valve at the pump or more likely at the foot valve in the bottom of the well needs to be replaced.
Carson Dunlop's sketch at left shows how a foot valve works and where it is installed. Replacing a foot valve in the well requires that the well be opened and the well piping be pulled out to permit removal of the old valve and installation of a new one.
After replacing the foot valve you should shock the well since you've probably contaminated it by laying your well piping and parts on the ground (and foot valves at the plumbing supplier are not kept in sterile containers). We discuss how to shock a well at WELL SHOCK / CHLORINATION PROCEDURE our WELL SHOCKING GUIDE
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Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
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