A flow restrictor is a device placed in the line of flow that reduces the space the water can flow through, which decreases the flow output in gallons per minute. Flow restrictors, flow regulators, and flow limiters are the same thing. They hold the flow to a steady rate, even when the upstream flow is highly variable.
Key Takeaways
- A flow restrictor creates a barrier that shrinks the area available to the flow, so fewer gallons per minute leave the pipe or hose.
- Flow restrictors do not measure flow; a flow meter measures the rate and can switch, batch, and totalize for process control.
- KOBOLD's star leaf-spring restrictor needs no power and holds flow constant between 29 and 145 PSI of differential pressure.
- A flow restrictor raises pressure upstream and reduces the gallons per minute, while the force and speed of the water increase.
- Installing a restrictor upstream of a flow meter reduces the turndown that the meter has to cover.
How Do I Reduce the Flow Rate of Water?
To reduce the water flow rate of domestic or industrial applications, devices called flow restrictors are used. They are placed into the line of flow and essentially reduce the space that the water can flow through. This in turn decreases the flow output, for example, a flow rate of 5 gallons per minute is reduced into a flow of 2 gallons per minute.
What Do Flow Restrictors Do?
Flow restrictors essentially create a barrier to the flow, decreasing the available area for the flow to move through. This decreases the flow output and fewer gallons per minute are released by the pipe or hose. Slowing down the flow rate cuts down the total water consumption/usage happening per minute.
A pipe or hose has a fixed cross-sectional area that the media flows through. Because of the fixed cross-sectional area, flow rate becomes a function of pressure where an increase in flow is a function of an increase in pressure. If you would like to control the flow within a fixed cross-sectional area with variable pressures, you need to accommodate the area in which the media flows.
To keep a constant flow, increasing pressure would need less cross-sectional area. This is where our REG Flow Restrictor excels. The passively activated, no power required, star leaf-spring mechanism decreases cross sectional area with an increase in pressure that keeps the flow rate constant. Our star leaf-spring will keep the flow constant between a differential pressure of 29 and 145 PSI.
The differential pressure curve below shows the principle with a 4 GPM example. Through a fixed orifice, the flow keeps climbing as the pressure climbs. Through the water flow restrictor, the flow rises with pressure only until the differential pressure reaches 29 PSI, then levels off at 4 GPM and holds there through 145 PSI.
| Differential pressure across the device |
Fixed orifice |
KOBOLD REG water flow restrictor (4 GPM example) |
| Below 29 PSI |
Flow rises as pressure rises |
Flow rises as pressure rises, up to the 4 GPM setting |
| 29 to 145 PSI |
Flow keeps rising as pressure rises |
Flow holds constant at 4 GPM |
What Does a Flow Restrictor Look Like?
Flow restrictors can look different based on the purpose and the model. The thing that they all have in common is that they are designed to restrict flow by reducing the available area for the flow to move through. The shape of the element that restricts can look different, what they are made of can be different, and where they are installed can be different. They generally will have the same common piping thread for installation that is used in the US, an NPT threaded connection.
What is the Difference between an Industrial Flow Restrictor and a Shower Flow Restrictor?
Shower flow restrictors are usually plastic and are not built for rigorous service. Industrial flow restrictors handle much higher pressures and temperatures, come in much larger line sizes with flanged or threaded connections, and hold the downstream flow rate constant even when the upstream flow varies widely.
Most shower heads purchased today will either have flow restrictors already installed/integrated within the shower head or will be included in the shower head package as an optional element to place within the shower head. This is to control water consumption and they have become more prominent in recent years due to an increased awareness of domestic water consumption.
Some shower flow restrictors are added as an additional link in the plumbing line itself, in between the shower head and the supply line. The housing for these will typically be metal like the supply piping, but the inside will be plastic. Both integral shower flow restrictors and added flow restrictors may offer multiple different plastic disks that are interchangeable and can be swapped out to allow different rates of gallons per minute flow. A typical flow rate for a water restrictor used in shower applications is 1.5 or 2.5 gallons per minute.
Industrial flow restrictors are used in a wide variety of industrial applications and deliver much higher pressure and temperature capabilities than simple shower restrictors. They also can be built for much larger line sizes and offer flanged connections in addition to threaded connections.
They are used anywhere that flow rates need to be held to a steady rate with no significant variation in the flow rate. Because flow restrictors only allow a predetermined amount of water through, the flow rate is constant on the downstream side of the device even if it is highly variable on the upstream side of the device.
Mechanical flow restrictors, like KOBOLD's, are self-actuating. The force of the flow in the pipe creates the energy for operation and they do not require power to operate, nor do they require any pneumatic lines. This reduces the total elements involved in flow restriction. There is less to break and cost savings are delivered by only requiring one element instead of multiple elements to restrict the flow. They will also operate in areas where there is no power source and will continue to operate if there is a localized power failure.
What is the Difference between Flow Restrictors, Flow Regulators, Flow Limiters, and Balancing Valves?
Flow restrictors, flow regulators, and flow limiters are used interchangeably. They are all ways to describe the exact same result that they deliver: restriction, regulation, and limitation of a flow. Sometimes the word "valve" is also added on to these first three terms as well. For example, flow restrictor valve. The word "valve" is a general term used very broadly for something that slows or shuts off flow. The tap to a garden hose is a "valve".
Balancing valves are sometimes also used as an interchangeable term for flow restrictors, but that is incorrect as their usual meaning is a bit different from the others. Balancing valves are used in HVAC applications to maintain certain flow conditions within a heating or cooling system to assure that the heating or cooling function is operating the same system wide. If a system is "balanced", it is operating correctly. If a system is "unbalanced", then it results in situations like some tenants of an apartment building being delivered too much heat and some tenants not receiving hardly any heat. Balancing valves also control flow, but the nuance of what they do is a little different than flow restrictors.
What is the Difference between a Flow Restrictor and a Flow Meter?
A flow regulator is a device that restricts and reduces the amount of liquid flowing through a pipe. For example, it can reduce a flow rate of 10 gallons per minute output to 5 gallons per minute output by reducing the space that the water is able to flow through. Flow regulators do not measure the rate of flow and cannot perform any additional process functions.
A flow meter is a device that monitors, measures, and controls the flow of liquid though a pipe. It calculates the rate that the media is traveling at and can also perform other process functions such as switching, batching, and totalizing to allow for process control. Sometimes, both flow meters and flow regulators are used in the same process line to measure and control the flow.
| Device |
What it does |
| Flow regulator |
Decreases the flow output |
| Flow meter |
Monitors flow; measures flow; helps control flow processes; can help start or stop flow; can deliver precision batching; can totalize flow volumes |
Where are Domestic Flow Restrictors Used?
- Shower Head Flow Restrictors
- Reduction of Water Flow in a Fountain
- Reduction of Water Flow from a Tap
- Reduction of Water Flow from a Garden Hose
- Flow Regulators for Washers
Where are Industrial/Commercial Flow Restrictors Used?
- Fluid Metering, Controlling Flow Throughput
- Actuator, Cylinder, or Motor Speed Control
- Inkjet Printing
- Medical Applications
- Chilled Water Balancing
- Semiconductors
- Reverse Osmosis Systems
- Water Flow Regulation for Stills
- Food and Beverage
How Do Flow Restrictors Work?
For our industrial flow restrictors, constant flow is achieved by two stainless steel spring plates that are crosswise mounted and riveted together. The gap between the spring-loaded stainless-steel plate and the seal-surface is continuously varied as the differential pressure changes. As the differential pressure decreases, the gap widens, and it closes as the pressure increases, thus maintaining a constant flow volume through the device.
Our flow restrictors are available for multiple line sizes, and they all use the same reliable passive restriction design. The labeled parts of the REG are listed below.
| KOBOLD REG flow restrictor component |
| Valve body |
| Pan |
| Spring star |
| Ring |
| Circlip |
Why Reduce Water Flow Rates with a Flow Restrictor?
For residential purposes flow restrictors can deliver cost savings by reducing unnecessary water use. For example, a shower producing 1.5 gallons per minute can probably do the job just as well as a shower producing 2.5 gallons a minute. The difference in the cost of one gallon per minute times the minutes your shower is running for a year can add up. As water scarcity becomes more prevalent in certain geographical areas and environmental concerns become more mainstream, it is considered responsible to eliminate any water wastage. Flow regulating valves can help in that goal.
The reasoning also stands true for industrial use. It can save money by reducing unnecessary water waste. In industrial applications they can also protect any sensitive equipment from spikes or lulls in flow rates and can better temper flow rates for any precision functions involved in the measurement process.
Is a Flow Restrictor Necessary?
It depends on whether the flow has to be held to a steady rate. A shower works without one, and the restrictor can usually be removed easily. In drought-prone areas a restrictor helps control water consumption, and in a process line it could be the answer to extreme flow variations, reducing the turndown a downstream flow meter needs.
For domestic applications, certain areas that are prone to drought have to strictly control water consumption. Flow restrictors can help lessen the amount used for each task and allow for more tasks to happen with the same amount of water use. In areas where water is not monitored as closely, they can still deliver cost savings.
Do you have to have one installed in your shower for your shower to function? No, they can usually be easily removed, either from inside the shower head or from the supply line. Removing them will effectively increase the flow output of your shower.
For industrial applications, if you require your flow to be held to a constant in your process line, a flow restrictor could be the answer to extreme flow variations. Reducing these variations reduces the necessary turndown requirements of any flow meters placed downstream of the flow restrictor.
Here is an example. Say a process line experiences a flow of 5 to 20 GPM but the desired flow meter for the process can only accommodate a maximum flow rate of 15 GPM. If a 15 GPM restrictor is installed upstream of the new flow meter installation, the turndown accommodation is now less, and the 5 to 15 GPM meter can be installed.
Does a Flow Restrictor Increase Pressure or Reduce it?
A flow restrictor will increase the pipe pressure on the upstream side of the restrictor. The increase in back pressure, coupled with the decrease in orifice size that the water can come through, results in a decrease in flow rate output (gallons per minute) but an increase in the flow speed and force.
A common example would be a garden hose. When it is flowing unobstructed from the bare hose end, the water does not travel very far, it basically falls out of the hose end and onto the ground. When a sprayer head is added to the garden hose, what happens? The water travels much farther with much more force, but less water is coming out of the hose per minute.
If you want to use the garden hose to fill up a bucket, will it fill up faster with the sprayer head on it or off it? Obviously, it will fill up faster without the restricting sprayer. But if you want to use the same hose to spray dirt off your sidewalk, do you want to use the open hose or a sprayer head? Obviously, a sprayer head is the best choice for this use because it delivers the water with an increased force and speed (but a decreased output of gallons per minute).
In short, a flow restrictor increases pressure on the upstream side of the restrictor. The flow output is decreased in water output per minute, but the force with which it comes out increases.
How Do I Install a Flow Restrictor?
A flow restrictor is installed inline: the supply line or pipe is opened, one pipe connects to the upstream side of the restrictor and one to the downstream side, and the inlet and outlet connections must match the line ends. The same process applies to domestic and industrial lines, and KOBOLD restrictors need no inlet or outlet runs.
For domestic uses, if a flow restrictor is not already integral to the appliance or device distributing water, a flow restrictor can be installed in the supply line before the device. To do this, the flow restrictor installation will need to be "inline". This means that the current continuous supply line will need to be disturbed or replaced. One pipe or tube will connect to the upstream side of the flow restrictor, and one will connect to the downstream side. This will effectively insert the flow restrictor into the supply line. Ensure that the inlet and outlet connections on the flow restrictor are compatible for connection with the supply line ends.
The same installation process applies to industrial applications. The flow restrictor is installed inline to the piping system through connections on the flow restrictor and connections on the pipe. To install our industrial flow restrictors, here are some guidelines.
- Remove any packaging parts left in the device.
- Make sure that the permitted maximum operating pressures and temperatures for the device are not exceeded.
- Install the flow limiter into the piping without mechanical stress.
- Protect the measuring pipe against external damage.
- Avoid pressure surges in the measuring pipe or blocking the flow quickly.
- If possible, after mechanical installation, make sure that the connection between screw connection and pipe is tight and does not leak.
- Inlet and outlet run: our flow restrictors do not require any inlet and outlet runs.
How Do I Remove a Flow Restrictor?
Flow restrictors that are not integral to shower heads are removed by unscrewing the device and reconnecting the two supply lines that were on either side of the device inlet and outlet. For integral flow restrictors, inspect the inside of the shower head and look for a small disc that is able to be removed.
What is an Inline Water Flow Restrictor?
Flow restrictors (flow regulators or limiters) are "inline" devices. This means that the body of the device is integrated into the piping system. Inline water flow regulators require pipe modifications to install into an existing line.
As opposed to flow meters, which can have insertion models where just the measuring element is inserted into the pipe through a hole, inline devices require that the piping be disassembled and reassembled with the device between an inlet side pipe and an outlet side pipe. Flow meters also come in clamp-on models, which are ultrasonic flow meters that are affixed to the outside of the pipe and the pipe is not disturbed in any way. Flow restrictors are generally "inline" devices only.
Where Do I Buy a Flow Restrictor?
KOBOLD's REG Automatic Flow Regulating Valve is available in either brass or stainless steel. It requires no power, is self-actuating, handles pressures up to 2,900 PSIG and temperatures up to 572 °F, covers water flow rates from 0.13 to 10.56 GPM with 3/4" NPT fittings, and is made in the USA.
How Much Do Flow Restrictors Cost?
Depending on whether your flow restrictor needs are domestic or industrial, flow restrictors can vary widely in cost. Simple plastic domestic flow restrictors can be purchased for less than $10. More rugged and industrial models will cost more but compared to most industrial instrumentation they are relatively cheap.
Who Makes Flow Restrictors?
KOBOLD is a global instrumentation company that designs, manufactures, sells, and supports a wide range of products for flow, level, pressure, and temperature. Our flow regulators are an all-metal construction, which ensures a long service life. To learn more about KOBOLD or to talk with one of our engineers, please call us now.
Learn more about why you should partner with KOBOLD for your application.
References
- U.S. Environmental Protection Agency, WaterSense. Showerheads. 2026. https://www.epa.gov/watersense/showerheads
Frequently Asked Questions
No. KOBOLD's mechanical restrictors are self-actuating: the moving water itself supplies the energy, so there is no power connection and no pneumatic line to run. That means fewer parts to break, one element instead of several, and a device that keeps working with no power source nearby or through a localized power failure.
The REG star leaf-spring holds the flow rate steady across a differential pressure of 29 to 145 PSI. Below 29 PSI the flow is still climbing with pressure. Once the differential reaches 29 PSI, the gap at the spring plate closes as pressure rises and opens as it falls, so the flow volume stays level up to 145 PSI.
Industrial flow restrictors generally use the NPT threaded connection that is the common piping thread in the US, and larger versions come with flanged connections for bigger lines. The KOBOLD REG comes in brass or stainless steel with 3/4" NPT female/female or female/male fittings.
Yes. Placed ahead of the meter, a restrictor tames the extreme swings in flow before they arrive, so the meter covers a narrower range. A line that swings from 5 to 20 GPM, for example, can use a 5 to 15 GPM meter once a 15 GPM restrictor goes in ahead of it.
No. KOBOLD industrial restrictors have no inlet or outlet run requirement, which is one reason they fit easily into an existing line. The main installation rules are to mount the device without mechanical stress, stay within its rated pressure and temperature, avoid pressure surges and sudden blocking of the flow, and check that the screw connection does not leak.
Because a flow restrictor only passes the amount of water it is set for, the flow rate on the downstream side stays constant even when the flow on the upstream side swings widely. In an industrial line this shields sensitive equipment from sudden surges or drops in flow and steadies the flow for any precision measurement that happens downstream.
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