Automatic Recirculation Valve Overview

Centrifugal Pumps Require Protection

If you use centrifugal pumps for any liquid-boiler feed water, condensate, or process fluids, a significant investment has been made in the pump, driver and related controls. Minimum flow protection is vital upon pump start up and low demand conditions. If reliable protection does not exist, the following unfavorable effects can interfere with the performance and reliable operation of the pump.

The liquid’s temperature will rise due to friction and hydraulic losses within the pump. Figure 2a illustrates the temperature rise in relationship to the H-Q curve. The curve indicates that at or near the best efficiency point, the temperature rise is minimal and not significant to the pump operation.

The process flow removes the generated heat from the pump. The temperature increases as the flow through the pump is reduced. Frictional and hydraulic losses generate heat, while the quantity of fluid to which this heat is transmitted is reduced. The rise in temperature results in the formation of vapor. The elevated temperature / vapor pressure of the liquid results in problems ranging from damaged seals and bearings to complete failure of the rotating elements.

Internal recirculation within the pump, often termed incipient recirculation, can cause a form of cavitation leading to impeller damage. Internal recirculation is illustrated in Figures 2b and 2c.

High specific speed pumps have power curves which rise as the flow reduces. If adequate flow is not maintained, motor overload will result.

Automatic Recirculation Valve Overvie

Widespread application on

  • Chemical industry
  • Petrochemical industry
  • Steel factory
  • Fire protection system
  • Traditional power plant
  • Paper-making industry
  • Shipment/shipping
  • Environmental protection industry

Minumum Flow Protection Methods

Continuous circulating system

The desired minimum flow volume is recirculated regardless of the system demand for fluid. Fixed orifices reduce the pressure before discharging. Continuous recirculating provides reliable pump protection, however, it is very inefficient and costly. The pump and driver must be sized to allow for the additional flow that is recirculating even when the flow demand rate exceeds the required minimum flow. See[Figure 3a]

Continuous circulating system

The desired minimum flow volume is recirculated regardless of the system demand for fluid. Fixed orifices reduce the pressure before discharging. Continuous recirculating provides reliable pump protection, however, it is very inefficient and costly. The pump and driver must be sized to allow for the additional flow that is recirculating even when the flow demand rate exceeds the required minimum flow. See[Figure 3a]

Instrument Controlled System

Recirculating occurs only when the process flow demand drops below the required minimum flow rate. Instrument controlled systems eliminate the inefficient and costly to operate constant recirculating systems. However, the necessary system components; check valve, flow meter, pressure reducing valve and related piping result in a considerable expense to purchase, install and maintain. See[Figure 3b]

Automatic Recirculating Valvesm

The automatic recirculating valve performs all flow sensing, bypass pressure reduction, reverse flow protection and modulating recirculating flow in an integral three port valve.The valve performs the same function of an instrumented system without the multitude of components, piping connections and system design expense. The valve is flow operated and does not require any air or electricity to operate. See[Figure 3c]

Figure 3b

ZD series Automatic Recycle pump protection valve

ZDT Model

  • Simple structure, low cost, long life, suitable for Low pressure
    Working conditions.
  • Cast valve body, material: carbon steel or stainless steel etc.
  • Big flow of bypass, maximum flow is 60% of main flow, KV value
    can be adjusted.
  • Bypass maximum operating pressure differential up to 4 MPa.
  • Pressure CL150# – 400#, size1’’ – 16’’.
ZDT Series Automatic Recycle Valve

ZDL Model

  • Multi-orifice cage bypass, low noise, suitable for middle and
    low pressure conditions.
  • Forged steel body, material: carbon steel or Stainless steel etc.
  • Non-return valve function is standard, Maximum pressure
    differential up to 6 MPa.
  • With venturi port main flow check valve structure, be applicable
    for complicated working conditions.
  • Pressure CL150# – 600#, size1’’ – 20’’.
  • Manual bypass operation is optional.
ZDL Series Automatic Recycle Valve

ZDM Model

  • Multistage decompression to preventing cavitation,reducing
    velocity, suitable for high pressure conditions.
  • Forged steel body, material: carbon steel or Stainless steel etc.
  • Non-return valve function is standard, Maximum pressure
    differential up to 30 MPa.
  • Pressure CL150# – 2500#, size1’’ – 20’’.
  • Manual bypass operation is optional.
ZDM Series Automatic Recycle Valve