An option for supplying water to a country house is to install an autonomous water supply system. To do this, there must be a well or well equipped with a pumping station on the site. However, it often happens that the aquifer lies quite deep. In such cases, instead of conventional equipment, an ejection pump is used, which can provide sufficient pressure in the system.
Why do you need an ejector?
If the water is deep, it is quite difficult to bring it to the surface. Experience shows that it is almost impossible to service wells with a depth of 7 m with a standard surface pump. Only powerful submersible devices, which are expensive and consume much more electricity, can effectively lift liquid to such a height. Thanks to such a device as an ejector, it is possible to modernize a surface pump, which costs several times less.
How the device works and how it works
The device uses Bernoulli's principle, from which it follows that an increase in the speed of fluid movement provokes the formation of a low-pressure area in close proximity to the flow (in other words, a rarefaction effect occurs). The ejector design includes:
- suction chamber;
- mixing unit;
- diffuser;
- special nozzle (gradually tapering pipe).
The liquid medium, moving through the nozzle, picks up a very high speed at its exit. The resulting vacuum provokes the flow of water from the suction chamber. The pressure of this portion of liquid is much greater. Having mixed inside the diffuser, the water begins to move through the pipeline in a common flow. Strictly speaking, the principle of operation of an ejector pump is the exchange of kinetic energy between flows that have different speeds (not to be confused with an injector, which acts exactly the opposite).
There are steam and steam jet ejection pumps. Vacuum-type steam apparatus maintain a vacuum by pumping gas out of a confined space. Most often, such devices are used to supply water.
Steam jet pumps operate by air ejection. Here, the energy of the jet is used, which arises in the process of pumping out an aqueous, vaporous or gaseous medium. Most often, river and sea vessels are equipped with steam jet pumps.
Where to install
The optimal location for the ejector is the pipe gap from the well to the pump. During the process of rising to the surface, a certain volume of water flows back towards the well. Once inside the ejector, it contributes to the appearance of a recirculation line. Developing significant acceleration at the exit from the nozzle, the flow carries along with it a certain amount of liquid from the well, creating additional vacuum inside the pipe. This allows the pump to save energy when lifting water from a significant depth.
To regulate the efficiency of the system, a valve is used on the recirculation line. With its help, you can change the amount of water that flows back into the well. That part of the liquid that is not used for recycling flows through pipes into the home. Another advantage of using an ejector is the self-suction of water. This allows you to further protect the equipment from idling, since surface-type pumps very often suffer from idling.
Types of ejectors
Having decided what an ejector is, you need to understand its varieties. Two types of devices are usually used to equip pumping stations. The first option involves incorporating the device into the design of the pumping device. In the second case, we are talking about separate placement. Each of these solutions has its own advantages and disadvantages that must be taken into account when organizing the system.
Built-in models
In this embodiment, the ejector is installed under the pump housing or next to it. This allows you not to look for additional space for it. All that is required is to implement the usual procedure for installing a pumping station. The closed housing provides the ejector with reliable protection from dirt and dust.
Pay attention! The process of creating a rarefied atmosphere and drawing back liquid is carried out in the pump itself. This eliminates the need to use additional filters. This approach makes the equipment very compact.
Such a pumping station with an ejector can draw water from a depth of up to 8 meters. It is capable of serving the territory of dacha farms, where the need for watering is especially acute. The weaknesses of indoor ejectors usually include noise during operation. For this reason, they try to install them away from living quarters (most often a separate room is allocated for this). The station's electric motor must have sufficient power to create recirculation.
Remote models
External installation of the ejector involves the use of an additional tank for pumping water. It creates the necessary working pressure and additional pressure difference, which reduces the load on the equipment. The ejector switching in such a scheme is carried out to the immersed section of the pipeline. This will require laying an additional pipe, which means the well will have to be made wider. As a result of this design solution, the system efficiency decreases by almost 35%.
On the other hand, this makes it possible to service wells up to 50 meters deep, significantly reducing the noise level during station operation. The place where it is located is often the house itself (its basement). The distance to the water intake point can be up to 40 meters, this does not affect the efficiency of the equipment. Such advantages make the external type ejection pump especially popular. All equipment is located in one prepared location, which increases its service life and ensures ease of maintenance and system setup.
Self-production
The design of the remote ejector is quite simple, which means it can be manufactured independently.
DIY assembly procedure:
- take a tee for a threaded internal connection. An outlet pipe with an upper fitting is screwed into its lower part so that the pipe does not look out from the back side (it is recommended to grind off the excess length and extend the missing length with a polymer tube). The optimal distance between the edges of the tee and the fitting is 2-3 mm;
- the upper section of the tee above the fitting is equipped with an adapter. The male end is designed to connect to the ejector base. The second end plays the role of a compression fitting for a metal-plastic tube designed to supply water from the well to the system;
- The lower part of the tee with the fitting is equipped with another fitting, which acts as an outlet for the recirculation pipe. This involves turning the bottom of the thread to 3-4 threads;
- the second branch is mounted in a side branch. It has a special collet for crimping the supply pipe from the well.
A polymer winding is used to seal threaded connections. On polyethylene pipes, the role of collets is played by crimping elements, where reverse shrinkage of polyethylene is used. Pipes of this type can be bent in any desired direction, which eliminates the need for angles. The finished ejector is connected in accordance with all recommendations.
Recommendations for maintaining and increasing device performance
Before installing the ejector pump, it is necessary to make the appropriate calculations. Its power must correspond to the depth of the well.
The pressure in the system is constantly monitored. If the station does not have a built-in pressure gauge, it should be installed. It is recommended to equip very deep wells with powerful equipment installed as close as possible to the water intake point. As a rule, such pumps have built-in ejectors.
If the depth of the well is between 15-40 m, it is advisable to use a remote ejector immersed in water.
The surface pump and the ejector are connected only by a vertical pipeline. Otherwise, the system will regularly become airborne, which will cause a decrease in its performance.
If you follow all the rules for installation and use, pumping equipment with an ejector will ensure a high-quality water supply, satisfying all the necessary needs both in the house itself and on the site.
An ejector is a device capable of transferring kinetic energy from one medium to another. An ejector for a pumping station helps lift water from sources more than ten meters deep and is used to protect the engine during a sharp drop in water level.
You can buy the device in a store or make an ejector for a pumping station with your own hands.
Operating principle
The ejector works on a fairly simple principle. The water is recirculated at the bottom of the pipeline, thereby filling the lack of pressure in the suction pipeline. The ejector pushes the water to the height from which the engine can draw it in.
The water coming out of the tapering T-shaped pipe is poured into the mixer at high speed from the suction chamber. In the diffuser, the normal flow of water is mixed with the accelerated one and enters the pipeline.
The ejector solves the problem of low pressure
An ejector is installed in the part of the pipeline located between the well and the pump. Part of the water flow that rises returns back to the well, and forms a constant recirculation on the way to the ejector. Additional vacuum occurs in the pipeline, and less pump energy is spent on lifting the liquid.
The operation of the system is adjusted using a valve. Part of the water is supplied to the house, the rest continues to be recirculated in the ejector. The pumping station starts up faster, energy consumption is reduced, and the installation of lower power equipment is required.
The package includes: diffuser, mixer, suction chamber, nozzle.
Types of ejectors
Water supply pumping stations for a private house or cottage are manufactured with an ejector built-in or separately mounted into the pipeline.
Stations with a built-in ejector are used for pumping water from shallow wells, storage tanks and other water sources. They are distinguished by their ability to capture water located below the pipe.
The built-in ejector is installed inside the pump. This solution makes it possible to significantly reduce the size of the station. In this case, installation of a filter is not required; the pump with a built-in ejector is not sensitive to sand particles suspended in the water. Such stations are primarily used for irrigation systems and with wells up to ten meters deep; it is not recommended to install them for water supply to residential buildings - they operate very noisily.
Pumping station with built-in ejector
When installing the ejector as a separate unit, an additional water tank is required to remove the load from the engine. The ejector is connected between the well and the engine to the part of the pipeline located in the water. For trouble-free operation of the device, two pipes are laid, as well as a pipe with a coarse filter and a check valve. To prevent airing of the system, pipes are installed strictly in a vertical position.
A station of this type operates almost silently and supplies water from wells up to fifty meters deep (optimal depth is from 15 to 20 meters). Pumping stations require the installation of filters to protect against the ingress of sand, silt, and clay impurities in the water.
The efficiency of stations with a remote ejector is small compared to a built-in one, but this disadvantage is compensated by the ability to supply water from considerable depths. Stations can be located several tens of meters from the source.
Self-production of an ejector
The cost of the ejector is quite high, and they are not always on sale. It is not difficult to make an ejector for a pumping station with your own hands.
Let's look at step-by-step instructions for self-manufacturing a conventional ejector, which can facilitate the lifting of water from wells up to 10 m deep, and is used for drawing water from greater depths.
Making an ejector is not a difficult task!
The following materials and tools will be required:
- A half-inch tee with internal thread is the main part;
- A half-inch fitting with a 12 mm or three-quarters 8-10 mm outlet, we will insert it inside the tee. Serves as a conductor of water under high pressure. To extend the fitting, you can use a vinyl chloride tube of the same diameter as the fitting;
- Adapter 20x25 mm with the necessary angles for further fastening to a pipe or three-quarters with an external thread at one end, and at the other end with a thread for a metal-plastic pipe with a diameter of 16 mm;
- Fitting;
- 90 degree corners for metal-plastic pipes:
- ¾ with external thread x ½ with internal thread;
- ¾ with external thread x 26 mm with internal thread for a metal-plastic pipe;
- ½ with external thread x 16 mm with internal thread for a metal-plastic pipe;
- Grinder, plumbing wrenches, adjustable wrench, sandpaper;
- A coupling with a three-quarter diameter (or clamp, screw) for straightening the threads on the fitting;
- A vice, but you can do without them.
If the well depth exceeds 10 m, it will be necessary to install an ejector of a more complex design, used in pumps with a power of more than 1 kW.
Diagram of elements of a homemade ejector
To manufacture such an ejector you will need the following parts:
- threaded pipe with a diameter of half an inch;
- ten-millimeter nozzle;
- tee E40;
- half-inch and three-quarter locknuts;
- check valve with coarse filter;
- plugs with holes and threads for fittings;
- half inch and three quarters cut;
- 90 degree bend half inch;
- nozzle or compressed copper tube with longitudinal holes and sealed seams.
First of all, it is necessary to grind off the hexagon of the fitting until it is shaped like a cone. The outer diameter of the fitting thread should be 2-3 mm larger than the lower base of the resulting cone. The length of the thread should be four turns. We cut off the excess length.
Then you need to align the threads, which will be disrupted when turning the part. We cut the thread longer so that it fits onto the cone and you can later screw it from any edge into the coupling or tee.
Screw the fitting into the tee until it stops. It should fit 2 mm upward into the tee outlet from the side.
There should be four or more turns left on the internal thread of the tee for attaching the outlet to them. If there are fewer turns left, grind the threads on the fitting until the required parameters are achieved. If the thread is short, you can add it to the required size using a vinyl chloride tube. The fitting should not protrude from the tee by more than 3 mm.
Ejector installation
If the device is installed in close proximity to the pump, then a pumping station with a built-in ejector is obtained.
In order for the system to work on the principle of a water supply pumping station for a private house with a remote ejector, you need to place it directly into a well or other source of water supply.
In this case, several pipes will be needed for installation:
- a pipe with an installed coarse filter is connected to the tee on the side and lowered to the very bottom;
- a pipe connected from below through which the emerging high-speed flow of water passes;
- the third pipe, which connects to the tee from above and is discharged into the water supply system, through which an accelerated flow of water passes under high pressure.
Ejector connection diagram
We screw an adapter with an external thread onto the tee from above. It should be located above the fitting. The second edge will serve as a connection to the pipe supplying water to the water supply. It will be secured with a fitting.
From below, we screw the corner elbow to the tee (into which the fitting was previously inserted) for further connection with the recirculation pipe. Fastening is done with a crimp nut.
We screw a corner into the tee on the side to connect it to the water supply pipe. We secure the pipe with a collet clamp.
We check the quality of fastenings and waterproofing.
All joints are sealed with tow or sealant.
We must install a check valve at the outlet. It will prevent liquid from flowing out of the suction pipe. If the water leaves, the system will not be able to work.
How to extend the service life of the ejector?
To extend their service life, pumping stations with an ejector must be operated in compliance with the following rules:
- When installing a station, it is important to correctly calculate the ratio of the power of the device and the depth of the source from which water is extracted.
- Constantly monitor the pressure in the pipeline. To measure the pressure in the system, you can use a pressure gauge used for car tires or purchase a station with a special built-in sensor;
- for sources with great depth, it is necessary to purchase a powerful pump, which must be installed as close as possible to the water intake;
- the use of a built-in ejector is justified only at high-power stations;
- when the source depth is from 15 to 40 meters, it is necessary to use a remote ejector installed inside the well and located in the water.
- When using a surface-type pump, it is important to correctly install the pipes coming from the surface of the ejector - strictly vertically. If the pipes are positioned incorrectly, air will enter the system and air pockets will form, which will negatively affect the operation of the system and reduce its service life.
If all operating rules are followed, ejector pumping stations operate uninterruptedly and provide tap water to the home, irrigation and other equally important household needs.
Video
Stefan from Bulgaria shared his experience of making a jet ejector with his own hands. This is his first ejector. The jet ejector is designed for gold mining. What you need to have for production. Well, this is at least the head and hands. Then comes the material and capabilities. If you have a machine and know how to sharpen, then half the job can be said to be done. All that remains is welding. A beautiful seam may not be necessary, but it is desirable. Maybe it would be easier to buy from Mikhalych or somewhere else? Maybe it's easier this way. Everyone makes their own decisions.
And today we’ll see how Stefan from Bulgaria made his first ejector.
And this is how it looks disassembled into parts.
Why did he make it this way? Why four cones? Yes, I just didn’t know how it would work and that’s why I did an experimental one. Mikhalych has put the production of ejectors on stream because everything has already been tested and the optimal option has been selected for a particular pipe diameter, pump and sluice. Or vice versa. Here is the first do-it-yourself jet ejector. Sharpen replacement cones and change them.
In principle, welding a pipe is not difficult for anyone who knows how to cook.
And another smaller pipe. We collect. We get a finished ejector.
A pumping station with an ejector is part of a water supply system that operates in autonomous mode. The principle of operation of the ejector is that it regulates in the pipe. In this case, water moves from the well to the surface - to the consumer.
The problem of low water pressure can be solved by installing an ejector for a pumping stationAll design elements are responsible for the energy efficiency of such a station. At the same time, water supply from a depth of 10 m or more is provided only by an ejector pump. Without this device, the station pumps water only from a well, the depth of which is a maximum of 7 m.
This article talks about both the types and design of an ejector and how to create an ejector pump.
Types and typical varieties of ejector pump
- - a vacuum pumping device that pumps gas out of a closed room and maintains a vacuum. Such a device is used in technical devices that provide water supply to consumers;
- steam jet - which uses the steam energy of a jet when pumping water, vapor or gas from an enclosed space. This device was used on river and sea vessels when pumping out water.
At the same time, the built-in pumping station produces a lot of noise, and the external ejector operates quietly.
All advantages and disadvantages directly affect the choice.
External ejector pumping stations are installed in a well located at great depth. They are connected to high power, which is installed indoors.
Internal pumping stations are connected to less powerful motors that are installed outside the house - where there is a shallow well (well).
Features and principle of operation of the installation
At factories producing wastewater disposal equipment, 2 types of pumping equipment are manufactured - with an internal and external ejector pump.
Devices with an internal ejection device pump out water from shallow (8 m or less) wells, reservoirs and wells.
A feature of such equipment is the presence of a “self-priming” function, as a result of which the water level is regulated, which is below the level of the inlet pipe. In this regard, before turning on the device, it is necessary to fill it with water.
Device diagram: 1- tee; 2 - fitting; 3 - vinyl chloride tube; 4 - adapter for metal-plastic pipe; 5 - NxMP angle; 6 - angle НхВ; 7 - NxMP angleAfter the device is filled with water and turned on, the impeller of the installation with an internal ejector pump sends water to the inlet of the ejector, thereby forming the necessary jet. It moves through a thin tube and the water pressure becomes faster.
When a pipe is connected to the inlet pipe, water begins to flow into the station.
The water then enters a chamber which sucks up the liquid. At the same time, the water pressure becomes less and the liquid flows through the diffuser to the outlet, slightly increasing the flow speed.
A device that uses an external ejector for a pumping station differs from an internal ejection pump in that it is used only at a depth of 10 m or more.
It is also difficult to install external ejector pumps on these devices. The pipes that connect the pumping devices to each other are installed only in a vertical position. Otherwise, a lot of air will get into the inlet line and it will stop working normally.
The optimal option for using devices with a remote ejector is to install the device at a depth of 20 m. As the lifting height increases, its performance decreases.
As a result, the external pumping device has less efficiency than the internal one.
Self-production of an ejector
In order to make an air ejector with your own hands, you need to purchase the following set of parts, consisting of fittings and mating elements:
- tee - the basis of the air ejector being designed;
- fitting – conductor of high water pressure in the device;
- couplings and bends - these elements are used for self-assembly of the ejector apparatus.
In order to assemble an ejector for a pumping station from parts with your own hands, you must perform the following steps:
- first, you should take a tee, the ends of which are used for threaded installation. In this case, the threads on its ends must be internal;
- Next, a fitting should be installed on the lower part of the tee. In this case, the fitting should be attached to the tee so that the small pipe is inside the pumping apparatus. In this case, the pipe should not appear at the end, which is located on the opposite side of the tee.
If the pipe turns out to be too long, then it must be shortened and sharpened.
In the same way, the short fitting is enlarged by using a polymer tube. The distance between the ends of the tee and the fitting should be 2-3 mm;
- then, on top of the tee - above the fitting, an adapter should be installed. Moreover, 1 end of the adapter must be made for an external thread (it must be installed on the base of the pumping apparatus), and the second must be installed as a crimp elbow (fitting) under a metal-plastic pipeline through which water flows from the well;
- At the bottom of the tee with the fitting installed, a 2nd crimp bend is installed, onto which the recirculation line pipeline must be put on and secured with nuts. In this regard, before installing the device, you must first grind the lower part of the fitting to 3-4 threads;
- Upon completion of the assembly of the homemade pumping apparatus, a second corner should be screwed into the branch on the side, at the end of which a collet clamp is installed for installing the water supply.
The connection using threads is made on seals made of polymers - fluoroplastic sealing material (FUM).
After completing the assembly of the homemade ejector pump, it is connected to the station itself.
If you install a homemade ejector outside the well, you will end up with a station with a built-in ejection device.
If the ejector device is installed in a shaft in which it is covered with water, you will get a station with an external ejection device.
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When installing such a homemade device, 3 pipes should be simultaneously connected to the tee:
- 1st - to the end, which is located on the side of the tee. The pipe is lowered to the bottom, and a filter with a mesh is installed at its end. A small pressure of water begins to flow through such a pipe;
- 2nd - to the end, which is located at the bottom of the tee. It is connected to the pressure line that leaves the station. As a result, the water flow rate in the ejector pump begins to increase;
- 3rd - to the end, which is located on top of the tee. It is brought to the surface and connected to a pipe that sucks in water. Through such a pipe, water will flow with even greater pressure.
As a result, the first pipe will be under water, and the second and third will be on the surface of the water liquid.
The price of an ejector for a pumping station ranges from 16-18,000 rubles. and depends on its technical characteristics.
In almost any area, a private house or cottage can be equipped with an autonomous water supply from a well or borehole. Typically, a pump is used to pump water. If the depth of the aquifer is less than 7 meters, then there will be no problems with choosing a pump. You can choose any unit of suitable power and performance. However, such products will not be able to lift water from deeper hydraulic structures. To lift water from great depths, it is necessary to use an ejector for a pumping station.
To understand why a pump ejector is needed, let’s imagine that we will improve a conventional submersible pump with our own hands to lift water from great depths. Certain limitations for the operation of a conventional pumping station will be created by water pressure, atmospheric pressure and the strength of the structural parts of the pump. During the modification, a conventional submersible pump will become much heavier and its dimensions will increase. As a result, such a unit will simply become difficult to operate. In addition, the amount of electricity consumed will increase significantly.
To avoid such problems, it is necessary to use additional parts to facilitate pumping water to a considerable height. It is the ejector that pushes the water towards the surface and facilitates its rise. This is a fairly simple device that you can install yourself.
Operating principle
To understand what an ejector is and to know its operating principle, it is necessary to study the purpose of the main components of the device. It consists of the following structural parts:
- A pipe with a narrow end called a nozzle. The water flowing through the nozzle acquires great acceleration and leaves this device at high speed. What is this for? The thing is that the flow of water at high speed does not exert such great pressure on the surrounding planes.
- Mixing device. Water from the nozzle enters this device. Here there is a significant discharge of the entire volume of liquid.
- Suction container. Under the influence of vacuum in the mixer, water from the well begins to flow into the suction chamber. After this, the mixed flow of liquid enters the next element - the diffuser.
- Diffuser. From this part of the structure, the liquid moves further through the pipeline.
You can install the ejector yourself. It is mounted in a pipeline laid from the well to the pumping device. The principle of operation of the unit is such that part of the liquid raised to the surface is lowered back into the hydraulic structure to the ejector. Thus, a recirculation line is formed. During such work, water bursts out of the nozzle at a powerful speed and takes some of the liquid out of the well, creating additional vacuum in the pipes. Thanks to this operating principle, pumping equipment spends much less power lifting water from great depths.
To regulate the volume of liquid returning back to the system, a special valve is installed on the recirculation line. Thanks to it, you can regulate the efficiency of the entire system.
It is important to know: part of the water that is not used in the recirculation system goes to the consumer. It is by these volumes that the productivity of pumping equipment is judged.
Advantages of ejector type pumps:
- there is no need to choose a unit with a powerful engine;
- the pumping part will not be so massive;
- this will ensure lower energy consumption and longer operation of pumping equipment;
- thanks to the ejector, it is easier to start all pumping equipment, since a small amount of water creates a sufficient vacuum in the pipes.
Features and types of design
There are two types of ejector type pump:
- with external ejector location;
- with internal (built-in) ejector location.
The choice of one or another type of ejector layout is determined by the requirements for pumping equipment. To suck air from different containers, another type of such units is used - an air ejector. It has a slightly different operating principle. In our article we will study devices to facilitate pumping water.
Internal ejector
Pumping equipment with a built-in ejector has more compact dimensions. In addition, the creation of liquid pressure and its intake for recirculation occurs inside the pumping equipment. This pump uses a more powerful motor that can recirculate liquid.
The advantages of this design solution:
- the unit is not sensitive to heavy impurities in water (silt and sand);
- the water entering the equipment does not need to be filtered;
- the device is suitable for lifting water from a depth of no more than 8 m;
- Such pumping equipment provides sufficient liquid pressure for domestic needs.
Among the disadvantages it is worth noting the following:
- this pump makes a lot of noise during operation;
- To install such a unit, it is better to choose a place away from the house and build a special room.
External ejector
To install the ejector externally next to the pumping equipment, it is necessary to equip a tank into which water should be collected. In this container the working pressure and the necessary vacuum will be created to facilitate the functioning of the pumping equipment. The ejector device itself is connected to that part of the pipeline that is immersed in the well. In this regard, there are restrictions on the diameter of the pipeline.
Advantages of a remote ejector:
- thanks to this design, it is possible to lift water from a significant depth (up to 50 m);
- it is possible to reduce the noise from the operation of pumping equipment;
- such a structure can be placed directly in the basement of the house;
- without reducing the efficiency of the pumping station, the ejector can be placed at a distance of 20-40 m from the well;
- Due to the fact that all the necessary equipment is in one place, it is easier to carry out repair and commissioning work, which contributes to a longer service life of the entire system.
Disadvantages of the external location of the ejector device:
- system performance is reduced by 30-35 percent;
- restrictions in the choice of pipeline diameter.
How to connect?
As a rule, the installation of pumping equipment with a built-in ejector is no different from the traditional installation of a conventional pump. To do this, it is enough to connect the pump inlet pipe to the pipeline coming from the well. A pressure line is also installed, a hydraulic accumulator and the necessary automation are installed.
In systems with an external ejector, the equipment is connected in the following sequence:
- To ensure recirculation, it is necessary to lay an additional pipeline from the inlet pipe of the ejector device to the pressure line of the pumping equipment.
- A pipe with a check valve is connected to the inlet of the ejector, on which a coarse filter is installed for pumping liquid out of the hydraulic structure.
If required, a control valve is installed in the recirculation pipeline. Such an additional device is simply necessary for wells in which the water level is above the calculated level of liquid for pumping equipment. Thanks to this valve, it is possible to reduce the pressure in the ejector and cause an increase in pressure in the water supply system. Some models are equipped with a built-in control valve.
It’s worth knowing: usually the adjustment method and location of the valve are specified in the instructions supplied with the unit.