Pressure reducing valve symbology: characteristics and representations

• Representation: valve body with spring/diagram above and flow arrow →.
• Technical reading: the fluid itself acts against the spring/diagram to maintain P2.
• Typical use: steam, industrial water, air networks; low complexity, high reliability (M1, M2, VD).

→ M1 pressure reducing valve

→ M2 pressure reducing valve

→ VD pressure reducing valve

• Representation: main valve + fine line to pilot (external control).
• Reading: better sensitivity and stability in the face of strong variations.
• Use: variable flow rates, more demanding set-points.

→This type of valve is not available in our catalog, but we can make them to order. Request information without any obligation.

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• Representation: balanced internal element; bellows may be indicated.
• Reading: compensates P1, reduces influence of fluctuations.
• Use: gases and steam with P1 oscillations (PRV30/44/45, M2+Bellows).

→PRV30 pressure reducing valve

→PRV44 pressure reducing valve

→PRV45 pressure reducing valve

→M2 pressure reducing valve with bellows

• Upstream strainer (Y-strainer): essential to protect seat/shutter.
• Pressure tap: at ≥10×DN downstream or according to data sheet.
• Pressure gauge: visualizes P2 and helps with calibration.

→Pressure reducing valves

→Pressure relief valves

→Control valves

Related articles:

Some of our most requested valves:

• What happens: a PRV/PSV opens only when the pressure exceeds the set point to depressurize; a reducer regulates continuously to maintain stable P2. Mounting a PRV where regulation is needed produces a sawtooth pattern, high consumption, and unnecessary trips.
  
• How to avoid it: define the objective of the loop. If you need constant downstream pressure (P2), choose a self-actuated reducer (e.g., M1/M2/PRV30/PRV45/VD). If the risk is overpressure, add a relief valve (S1/S2/S3 or PRV53/54/55) in parallel or in the critical equipment.

• What happens: entrained particles erode the seat/shutter, generate leaks, loss of tightness, and deviations from the set-point. In steam, scaling accelerates wear.
  
• How to avoid it: install a strainer filter (Y-strainer) upstream of the valve, with a mesh according to the fluid (indicative: 80–200 mesh in clean water; more open in steam/air). Provide for purging and periodic maintenance of the sieve. Leave a straight section ≥5–10 DN before the reducer.

• What happens: if the tap is too close to the valve, after a curve, a T, or a turbulence zone, hunting (oscillations) and poor repeatability may appear. In networks with variable flow, measuring at the wrong point unbalances the entire loop.
  
• How to avoid it: place the tap 1–5 DN downstream in a straight line, away from disturbances (curves, pumps, on/off valves). In long lines or with distributed consumption, use a remote tap at the point where P2 matters (e.g., inlet of a heat exchanger). Use a clean, purgeable, and as short as possible impulse tube.

• What happens: without revisions, the strainer becomes saturated, the spring fatigues, and the seals degrade; P2 ceases to be stable.
  
• How to avoid it: schedule an annual inspection (or according to severity), condition of seat/shutter, seals, spring/diaphragm, external leaks, strainer cleaning, and set-point verification. Use original kits to maintain performance and certifications.

• What happens: a valve “at line size” is usually oversized, works almost closed, vibrates, and cavitates; or vice versa, it falls short and throttles.
  
• How to avoid it: calculate the Kv/Cv with Q, ρ, P1, P2, and T; choose the DN that meets capacity, noise/cavitation, and reasonable pressure drop. If the Qmin is very low, consider a reduced trim or two valves in parallel (one “peak” and one “base”).

• What happens: mounting outside the recommended orientation or reversing the flow generates noise, vibrations, and premature wear.
• How to avoid it: respect the flow arrow, mount horizontally with the actuator vertical when the model requires it, leave maintenance space and straight sections before/after.

• What happens: selecting “by eye” leads to inadequate spring ranges (without margin) and to seats/closing classes that do not meet the leakage requirements (e.g., for drinking water or gases). Result: imprecision, spring overstress, and leaks when stopped.
• How to avoid it: define in the specification:
  • P1 max. / P2 set / ΔP operating and flow range (Qmin–Qmax).
  • Spring range required (e.g.: 0.5–3; 1–8; 4–12 barg, etc.).
  • Closing class (metal-metal or soft: NBR/EPDM/PTFE), chemical compatibility, and temperature.
    Regulations (PED/CE, ATEX if applicable) and connections (DIN/ANSI/BSP/NPT).
  • Ask the manufacturer for the dimensioning sheet by Kv/Cv and the correct spring with margin (set between 30–70% of the range).

If you have any questions or need help with everything related to the symbology of reducing valves or which model is the most suitable for your system, do not hesitate to fill out the contact form; we will be happy to assist you.

Our technical team can review your process data (fluid, flow rate, P1/P2, temperature), propose the most efficient solution, and provide you with clear recommendations on materials, connections, and closing class.

We can also guide you in the interpretation of drawings and standards, and prepare a customized proposal if your installation requires it. Write to us and we will respond with practical and direct advice.