No. A pressure control valve regulates pressure at a defined point, while a flow control valve regulates or limits the rate of water passing through a pipeline. A pressure reducing valve (PRV) controls downstream pressure. A float valve responds to tank level. These valves can affect both pressure and flow, but their control targets and feedback signals are different.
For a pressure control valve vs flow control valve comparison, start with the required result: a pressure setting in bar, a flow setting in m³/h, or a tank level. The valve body alone may not tell you which function it performs.
Pressure control valve vs flow control valve at a glance
| Comparison | Pressure control valve | Flow control valve | Float valve |
|---|---|---|---|
| Controlled variable | Downstream pressure, upstream pressure, or differential pressure, depending on configuration | Flow rate or maximum permitted flow | Liquid level |
| Typical setting | bar, kPa, or psi | m³/h, L/s, or GPM | Level or high/low switching points |
| Feedback | Pressure acting on a regulator or pilot, or a pressure transmitter and controller | Flowmeter feedback, differential pressure across a measuring restriction, or a compensation mechanism | Float movement, directly or through a pilot |
| Common water-system duty | Pressure reduction, pressure sustaining, or pressure relief | Branch flow limitation, process-water regulation, or controlled filling | Tank or reservoir filling |
| What it does not automatically guarantee | A fixed flow rate | A fixed downstream pressure | A fixed inlet pressure or filling rate |
All automatic regulating functions depend on adequate available pressure, suitable sizing, and the operating limits of the selected valve.
For a broader application overview, see our flow control valve, pressure reducing valve, and float valve selection guide.
What does a pressure control valve control?
“Pressure control valve” describes a family of functions. Specify which pressure the valve must control and where it is measured.
Pressure reducing valves control downstream pressure
A PRV throttles the water supply to maintain a lower pressure downstream. When demand increases and downstream pressure falls, it opens further. When demand falls and downstream pressure rises, it moves toward closure.
The outlet pressure setting does not specify how much water users must consume. Flow can vary while the valve regulates pressure.
In a PRV water system, the valve also needs sufficient inlet pressure and capacity. It cannot raise a weak supply to a higher outlet pressure.
Norite’s F8020 pressure reducing valve is a product reference for this control duty. Confirm the operating range and required pilot configuration for the project.
Pressure sustaining valves protect upstream pressure
A pressure sustaining valve restricts delivery to a downstream branch when upstream pressure approaches its minimum setting.
For example, a tank filling line may draw so much water that nearby users lose pressure. Upstream pressure sustaining can reduce tank filling to preserve pressure in the supply zone, provided the source itself can support that zone.
A downstream PRV alone does not provide this upstream control function.
Pressure relief valves discharge excess pressure
A pressure relief valve opens a discharge path when pressure exceeds its setting. Its installation and purpose differ from a PRV installed in series with the supply.
Write “pressure reducing valve” or “pressure relief valve” in specifications. The abbreviation PRV can otherwise cause confusion. In this article, PRV means pressure reducing valve.
How does a flow control valve work?
A flow control valve changes its opening to regulate the amount of water passing per unit time. However, a manually adjusted restriction and an automatic flow regulator behave differently.
A fixed opening does not guarantee fixed flow
A throttled manual valve establishes a resistance. If the pressure difference across that resistance changes, flow generally changes too.
A valve adjusted to pass the desired flow during commissioning may pass a different flow when pumps switch, reservoir levels change, or other branches open.
For stable flow under changing conditions, specify an automatic regulating function and its permitted operating range.
Automatic flow control needs suitable feedback
An electronic system can use a flowmeter, controller, and actuated valve. The controller compares measured flow with the target and adjusts valve position.
A hydraulic system can use differential pressure across a measuring orifice to operate a pilot valve. This arrangement can regulate flow without an electronic flow transmitter or external electrical power.
The complete control arrangement matters. A regulating valve body fitted with an actuator does not automatically become a constant-flow controller.
Review the flow regulating valve and piston valve options together with the sensing and control equipment required for the duty.
Flow limiting and constant-flow regulation are different requirements
A maximum-flow limiter prevents delivery above a selected ceiling. Flow may remain below that ceiling when demand is lower or available head is insufficient.
A constant-flow control loop attempts to maintain a target flow, but it still requires a receiving system that can accept the water and enough available pressure.
Neither arrangement can force the specified flow through a closed downstream isolation valve.
Why changing pressure can change flow
Pressure difference drives water through pipeline resistance. A control valve changes that resistance as it moves.
For water under suitable turbulent, non-choked flow conditions, a simplified valve relationship is:
Q = Kv × √(Δp / SG)
Where:
- Q is flow in m³/h.
- Kv is the flow coefficient at the actual valve opening.
- Δp is the pressure difference across the valve in bar.
- SG is the liquid’s specific gravity relative to water.
This relationship explains why a fixed valve opening cannot reliably hold the same flow when differential pressure changes.
It also explains why a flow control valve produces a pressure drop. That pressure drop is part of regulating flow; it does not establish an independent downstream pressure setting.
The equation is a preliminary hydraulic relationship. Final selection needs manufacturer data, including control range and cavitation limits. Our pressure reducing valve sizing guide covers the operating data needed for that assessment.
Can a pressure reducing valve replace a flow control valve?
A PRV is suitable when the requirement is controlled downstream pressure. It cannot generally replace a dedicated flow-control function when the specification requires a measured flow target or maximum-flow limit.
Consider an illustrative water branch with these design targets:
| Requirement | Illustrative value |
|---|---|
| Inlet pressure | 8 bar |
| Required downstream pressure | 3 bar |
| Maximum permitted branch flow | 20 m³/h |
These values explain control behavior; they are not a valve sizing recommendation.
A PRV set to 3 bar will attempt to maintain that pressure as demand varies. If the downstream system can draw more than 20 m³/h at 3 bar, a standard pressure-reducing function will not enforce the flow ceiling.
A separate or combined flow-limiting function is needed to impose that limit.
Conversely, a flow limiter set to 20 m³/h does not guarantee 3 bar downstream. Outlet pressure depends on inlet conditions, valve losses, and the downstream system.
Can one valve control both pressure and flow?
Yes. A main valve can have both pressure-reducing and flow-limiting pilots, or an electronic control arrangement with defined pressure and flow priorities.
With a typical combined pressure-reducing and maximum-flow-limiting valve:
- Below the flow ceiling, the pressure function regulates downstream pressure.
- When demand would exceed the ceiling, the flow-limiting function restricts delivery.
- Downstream pressure may then fall below the pressure setting.
This is expected behavior when flow limitation takes priority. One throttling element cannot independently satisfy two incompatible targets.
For the illustrative branch above, maintaining 3 bar may require more than 20 m³/h. Enforcing the 20 m³/h limit can therefore prevent the system from maintaining 3 bar.
Specify which requirement has priority and how the valve should respond when the targets conflict.
Where does a float valve fit?
A float valve controls liquid level. In a tank filling application, rising water moves the float toward the closing position; falling water allows filling to resume.
A modulating arrangement adjusts inflow around a target level. An on/off arrangement fills between defined switching levels.
Although a float valve throttles flow and creates a pressure drop, its basic control signal is tank level. It does not independently hold a pipeline pressure setting or a maximum filling rate.
A tank inlet may therefore need several functions:
| Tank filling requirement | Function to assess |
|---|---|
| Stop or reduce filling at the required level | Float or other level control |
| Limit the filling rate | Flow limitation |
| Reduce excessive pressure before the filling valve | Pressure reduction |
| Preserve pressure for upstream users | Pressure sustaining |
Some automatic valves combine these functions. Others use separate components. The hydraulic design must establish the control priorities and available pressure through the complete arrangement.
See Norite’s float valve for the level-control product category.
Which valve fits your water system?
| Application or problem | Control function to assess | Main selection check |
|---|---|---|
| Building inlet supplied at excessive pressure | Pressure reducing | Outlet requirement at peak demand and low-flow stability |
| Branch must stay below an agreed delivery rate | Maximum-flow limiting | Flow ceiling and available differential pressure |
| Treatment process requires a steady feed rate | Automatic flow regulation | Flow measurement, turndown, and downstream acceptance |
| Tank keeps filling after reaching the desired level | Level control | Float travel, shutoff performance, and independent overflow provision |
| Tank filling lowers pressure in a shared supply | Pressure sustaining, potentially combined with level control | Upstream pressure priority |
| Branch needs reduced pressure and a maximum-flow cap | Combined pressure reduction and flow limitation | Behavior when the flow ceiling becomes active |
| Pump switching causes pressure spikes | Transient assessment and suitable surge protection | Pressure history and system response |
A pressure gauge reading alone is rarely enough to diagnose a delivery problem. Record flow and pressure together under the condition that causes the complaint.
Installation and commissioning checks
Measure pressure at the relevant locations
Record inlet and outlet pressure while water is flowing. A satisfactory static inlet reading can conceal a supply limitation at peak demand.
For flow control, provide a reliable way to verify actual flow. Follow the selected flowmeter or measuring-orifice requirements for orientation and straight pipe lengths.
A downstream pressure reading also depends on its location. Account for elevation and pipe losses between the valve and the user that needs a minimum service pressure.
Protect the control circuit from debris
Pilot passages and sensing lines can become blocked by installation debris or deposits. Provide the filtration specified for the valve and allow access for cleaning.
A mainline strainer also consumes pressure head. Its dirty condition can leave the control valve with too little differential pressure.
Use our Y strainer installation position guide when planning protection and maintenance access.
Check low flow and cavitation separately
A valve sized only for peak flow may regulate poorly at minimum demand. Confirm the manufacturer’s minimum stable operating range.
High pressure reduction can also cause cavitation. Assessment requires the actual inlet and outlet pressures, water temperature, and valve-specific limits. Anti-cavitation trim or staged pressure reduction may be needed.
Cavitation and water hammer require different assessments. A PRV should not be assumed to solve every pressure transient.
Test more than one operating point
Commission at representative low, normal, and high demand. For combined controls, verify the transition into flow limitation and record the resulting downstream pressure.
Check behavior as a tank reaches its closing level and when pumps change operating state. Follow the manufacturer’s adjustment procedure.
If pressure continues to fluctuate, use the PRV valve troubleshooting guide to investigate the supply, pilot circuit, strainers, and valve condition before repeatedly changing settings.
What to include in a control valve enquiry
Send operating conditions with the requested valve function.
| Information | What to provide |
|---|---|
| Control objective | Downstream pressure, upstream pressure, flow target, flow ceiling, or tank level |
| Control priority | Which requirement takes priority when several functions interact |
| Water conditions | Water type, temperature, suspended solids, and relevant chemistry |
| Flow range | Minimum, normal, and maximum flow |
| Pressure conditions | Maximum static pressure and dynamic inlet/outlet pressures at the stated flow points |
| Pipeline details | DN, pipe material, flange standard, and pressure class |
| System arrangement | Pump operation, tank elevations, branches, and downstream equipment |
| Controls | Hydraulic operation, electrical supply, signals, and required failure response |
| Verification | Datasheet, capacity curves, operating limits, functional test requirements, and installation manual |
A pressure rating and pipe diameter do not define a regulating duty. A shell or seat test also does not demonstrate that the valve will maintain the required pressure or flow across the project’s operating range.
Frequently asked questions
Is a pressure control valve the same as a pressure reducing valve?
A pressure reducing valve is one type of pressure control valve. Pressure sustaining and pressure relief are other pressure-control functions. Specify the function and sensing location.
Does a pressure regulator affect water flow?
Yes. Its movement changes resistance and can change flow. A standard pressure regulator uses pressure feedback, so its setting does not guarantee a particular flow rate.
Will a flow control valve reduce pressure?
A throttling flow control valve creates pressure loss while water passes through it. Maintaining a specified downstream pressure requires an appropriate pressure-control function.
Do automatic water control valves need electricity?
Some do. Electronic control needs a suitable power supply, while direct-acting regulators and many hydraulic pilot-operated valves use fluid pressure and mechanical components. Hydraulic operation still requires the pressure conditions specified for the model.
Can a float valve replace a PRV?
A basic float valve provides level control. Where tank filling also requires pressure reduction, specify a separate PRV or a valve with both functions.
Can I select the valve from pipe size alone?
No. Selection also needs the required control function, flow range, available differential pressure, water conditions, and manufacturer operating limits.
Discuss your water-system control requirements
Norite offers water-system valves and related equipment, including pressure reducing, flow regulating, and float valve categories.
Contact Norite with your pressure readings, minimum and maximum flow, pipeline size, and control priorities so the proposed valve configuration can be reviewed against the actual duty.
