Series 120 Rate of Flow Control Valves

Series 120 Rate of Flow Control Valves

The OCV Series 120 Rate of Flow Control Valves is designed to control or limit flow to a predetermined rate, regardless of fluctuations in downstream or upstream pressure.

Series 120 Rate Of Flow Control Valves

Valve Features

  • Operates automatically off line pressure.
  • Heavy-duty, nylon-reinforced diaphragm.
  • Rectangular-shaped, soft seat seal provides drip-tight Class VI closure.
  • Diaphragm assembly guided top and bottom.
  • Throttling seat retainer for flow and pressure stability.
  • Easily maintained without removal from the line.
  • Replaceable seat ring.
  • Alignment pins assure proper reassembly after maintenance.
  • Valves are factory tested.
  • Valves are serial numbered and registered to facilitate replacement parts and factory support.


Where two water districts are connected, the valve limits flow rate between the two.

Water Distribution System


Installed in the backwash line, the valve limits flow rate during the backwash cycle to prevent filter media blow out.

Filter Backwash Control

Valve Operation


  • The OCV Model 120 rate-of-flow control valve is designed to control or limit flow to a constant, predetermined rate regardless of fluctuations in upstream or downstream pressure. It consists of the following components.
  1. Model 65 Basic Valve, a hydraulically-operated, diaphragm-actuated, globe or angle valve with an elastomer-on-metal seal and throttling seat retainer.
  2. Orifice Plate, installed integral to the main valve’s inlet flange. The orifice plate is the flow-sensing device for the rate-of-flow pilot. Orifice plate bore is sized for application flow range.
  3. Model 2450 Rate-of-Flow Control Pilot, a two-way, normally-open pilot valve that senses the differential pressure created across the orifice plate and balances it against an adjustable spring load. This differential is proportional to the flow rate through the valve. An increase in differential tends to make the pilot close.
  4. Model 126 Ejector, a simple “tee” fitting with a fixed orifice in its upstream port. It provides the proper pressure to the diaphragm chamber of the main valve depending on the position of the rate-of-flow pilot.
  5. Model 141-2 Needle Valve, that controls the opening and closing speed of the main valve.
  6. Model 159 Y-Strainer (standard on water service valves), The strainer protects the pilot system from solid contaminants in the line fluid.
  7. Two Model 141-4 Ball Valves (standard on water service valves, optional on fuel service valves), useful for isolating the pilot system for maintenance or troubleshooting.


Rate Of Flow Control Valve Operation



The OCV Model 128, excess flow shut-off valve closely resembles the standard model 120 Rate-of-Flow control valve. However, in place of the previously described rate of flow pilot model 2450, the 128 is equipped with an adjustable, spring-loaded, locked-open pilot that is non-modulating (model 1380). As long as the differential pressure across the orifice plate (flow rate) is less than the pilot setting, the valve remains open. Should the orifice plate differential exceed the setting of the pilot, the pilot “trips” closed and fully closes the main valve. The pilot and main valve remain closed until manually reset.

Excess Flow Shut-Off Valve

The OCV Model 128 is therefore valuable in protecting against a break in the downstream pipe.

Model 1380 Excess Flow Pilot Material of Construction: Stainless Steel
Orifice Plate: Stainless Steel



Based upon standard orifice plate bore size with water as the flowing media. Consult factory for other liquids and flow rates.

Rate of Flow Sizing Characteristics Chart

Sizing Rate of Flow Control Valves

Using the flow characteristics chart above, select the size where the design flow rate comes closest to the middle of the flow range shown. For example, for 300 gpm, the best size would be a 3″.

Sometimes a valve selected in this manner will be less than line size, and there may not be room for reducers. By changing to a small-than-standard orifice plate, larger valves can be used at lower flow rates than those shown. Consult factory for details. For a comprehensive guide to sizing, refer to OCV ValveMaster Sizing & Selection software.


  • Pilot is field adjustable (within orifice bore range).
  • Large diaphragm area for sensing small changes in differential pressure.
  • Hydraulically balanced design for accurate control.
  • Specifically designed for rate of flow control.


The 120 is furnished fully factory-assembled and ready for installation at the appropriate point in the system. Install the valve referencing the flow arrow tag. The orifice plate will be in the inlet flange. It is recommended that at least five diameters of straight pipe be allowed upstream of the valve.


The model 2450 is a normally-open, double-acting, spring-loaded, diaphragm pilot valve (see illustration). Control piping provides for sensing differential pressure across the valve inlet orifice plate. The upstream (high pressure) side is sensed under the pilot diaphragm; the downstream (low pressure) side over the diaphragm. Closing of the pilot is assisted by the adjustable spring. Flow rate may be changed by the adjusting screw. The pilot is adjustable within a 4:1 ratio, depending on the orifice size used. Variations in pressure differential across the orifice plate produce modulation in the double-acting pilot, which in turn creates a mirror-modulation in the main valve. Increased differential pressure works to close the valve while a drop in such pressure opens it.

  1. Adjusting Screw Cover
  2. Adjustment Screw
  3. Spring
  4. Diaphragm
  5. Orifice Plate Low-Pressure Sensing Port
  6. Orifice Plate High-Pressure Sensing Port
  7. Pilot Inlet
  8. Pilot Outlet

Rate of Flow Pilot

Valve Selection Guide

By combining various control pilots, multiple valve functions can be performed on a single Series 120 Rate-of-Flow Control Valve. To find the combination function valve, select the desired features and then the model number. This chart shows only a sample of those most often specified valves. Consult the factory for specific data on the model you selected.

Combination valves can often reduce or eliminate other equipment. Example: If the system requires a Pressure-Reducing function, the feature can be added as a function of the Rate-of-Flow Valve, Model 120-2.

Valve Section Guide

Material Specifications

Rate Of Flow Control Valves Specifications


Rate Of Flow Control Valves Dimensions Table

For maximum efficiency, the OCV control valve should be mounted in a piping system so that the valve bonnet (cover) is in the top position. Other positions are acceptable but may not allow the valve to function to its fullest and safest potential. In particular, please consult the factory before installing 8″ and larger valves, or any valves with a limit switch, in positions other than described. Space should be taken into consideration when mounting valves and their pilot systems.


A routine inspection & maintenance program should be established and conducted yearly by a qualified technician. Consult our factory @ 1-888-628-8258 for parts and service.

Rate of Flow Control Valves Dimensions


When Ordering please provide:
Series Number – Valve size – Globe or Angle – Pressure Class – Screwed, Flanged, Grooved – Trim Material – Adjustment Range – Pilot Options – Special needs / or installation requirements.