As the world leader in constant force spring technology, John Evans’ Sons (est. 1850) has produced well over 100 million high-performance constant force window balance products.

The following innovations are the result of John Evans’ Sons unparalleled experience and technical expertise in window springs.

Patent Information by product series.

Di FLEX 500 BALANCE SERIES

…The most flexible constant force balance system for 1/2” sash windows.

Offers the following:

  • Ability to transition from a fixed coil balance to an inverted coil balance by simply changing the mounting orientation and attaching a mounting clip to the coil spring.
  • Reduced SKUs, springs are pre-assembled in holders (singles and doubles), and quickly make triple and quad assemblies by connecting the spring assemblies.
Di FLEX 500 Balance System Download .pdf
Di FLEX 500 Balance System

1/2″ Series Drop-In Balance System Introduction

Di FLEX 500 Balance System Download .pdf
Di FLEX 500 Balance System

1/2″ Series Drop-In Balance Components

Di FLEX 500 Balance System Download .pdf
Di FLEX 500 Balance System

1/2″ Series Drop-In Balance FIXED CONFIGURATIONS Fabrication Instructions

Di FLEX 500 Balance System Download .pdf
Di FLEX 500 Balance System

1/2″ Series Drop-In Balance INVERTED CONFIGURATIONS Fabrication Instructions

Di FLEX 500 Balance System Download .pdf
Di FLEX 500 Balance System

1/2″ Series Drop-In Balance FIXED CONFIGURATIONS 4 Step Assembly Procedure

Di FLEX 500 Balance System Download .pdf
Di FLEX 500 Balance System

1/2″ Series Drop-In Balance INVERTED CONFIGURATIONS 4 Step Assembly Procedure

Di FLEX 500 Balance System Download .pdf
Di FLEX 500 Balance System

1/2″ Series Drop-In Balance INVERTED CONFIGURATIONS Clip-less Assembly Procedure

Di FLEX 500 Balance System Download .pdf
Di FLEX 500 Balance System

1/2″ Series Drop-In Balance FIXED CONFIGURATIONS Weight Chart

Di Flex 500 Fixed Assembly Demo

Di Flex 500 fixed configuration assembly demo video.

Di Flex 500 Inverted Assembly Demo

Di FLEX500 inverted configuration assembly demo video.

Di SERIES for 3/4″ SASH WIDTHS

…the most technologically advanced Drop-In balance system for hung windows.

Di SERIES for 3/4" SASH WIDTHS the most technologically advanced Drop-In balance system for hung windows.

Offers the following:

  • Low cost and a reduction of on-hand inventory
  • Quiet operation with low operating forces
  • Superior cam strength & reliability
  • Higher-weight AAMA-qualified springs
  • Patents: see link above
Di-750 Balance System Download .pdf
Di-750 Balance System

3/4″ Series Drop-In Balance System Introduction

Di-750 Balance System Download .pdf
Di-750 Balance System

3/4″ Series Components & Configurations

Di-750 Balance System Download .pdf
Di-750 Balance System

3/4″ Series 4 Step Assembly Procedure

Di-750 Balance System Download .pdf
Di-750 Balance System

3/4″ Series Fabrication Instructions

Di-750 Balance System Download .pdf
Di-750 Balance System

3/4″ Series Spring Load Chart

SFI (Static Friction Inverted) Constant Force Balance System

…a better option for one inch pocket windows.

SFI logo- SFI (Static Friction Inverted) Constant Force Balance System a better option for one inch pocket windows.

Our SFI Constant Force Balance System uses AAMA-qualified springs and is a simple conversion from block & tackle.

The SFI Constant Force Balance System:

  • Designed for a one-inch pocket
  • As few as three SKUs
  • Egress achieved
  • Low operating forces
  • Carrier design provides static friction
    (eliminates sash drift)
  • Patents: see link above
Static Friction Inverted Series Download .pdf
Static Friction Inverted Series

SFI Series Introduction

Static Friction Inverted Series Download .pdf
Static Friction Inverted Series

SFI Series Features Comparison

SFI Field Service Demo

SFI field service demo video.

SideLoad™ Constant Force Balance System

…a better option for side load windows.

 SideLoad™ Constant Force Balance System a better option for side load windows.

Our SideLoad™ Constant Force Balance System uses AAMA-qualified springs and is a simple conversion from block & tackle.

Compared to block & tackle, the SideLoad™ Balance System offers:

  • A lower price
  • Significantly reduced operating forces
  • A substantial reduction of on-hand inventory
  • Dramatically smaller space requirements
  • A tighter-fitting sash
  • Patents: see link above
SideLoad Balance System Download .pdf
SideLoad Balance System

SideLoad Balance NEW FEATURES

SideLoad Balance System Download .pdf
SideLoad Balance System

SideLoad Balance Introduction

SideLoad Balance System Download .pdf
SideLoad Balance System

SideLoad Installation Instructions

SideLoad System Sash Cam Download .pdf
SideLoad System Sash Cam

Sash Cam Dimensions & Mounting

SideLoad Balance System Download .pdf
SideLoad Balance System

Slot Milling Instructions

SideLoad Balance System Download .pdf
SideLoad Balance System

One Piece Sash Guide Instructions

SideLoad Balance System Download .pdf
SideLoad Balance System

Two Piece Sash Guide Colors

SideLoad Balance System Download .pdf
SideLoad Balance System

Spring Carrier 2-Stage Lock System

SideLoad Balance System Download .pdf
SideLoad Balance System

Field Installation Instructions

SideLoad Balance System Download .pdf
SideLoad Balance System

SideLoad Spring Selection Guide

SideLoad™ Constant Force Balance System for WOOD

SideLoad Balance for WOOD Download .pdf
SideLoad Balance for WOOD

SideLoad for WOOD Introduction

SideLoad Balance for WOOD Download .pdf
SideLoad Balance for WOOD

SideLoad for WOOD Installation Instructions

The SideLoad™ Balance System – Demo

The SideLoad™ Constant Force Balance System - Demo Video.

The SideLoad™ Balance – Sash Removal & Component Review

The SideLoad™ Balance - Sash Removal & Component Review Video

The SideLoad™ Balance – Sash Guides & NEW Sash Cam Demo

The SideLoad™ Balance - Sash Guides & NEW Sash Cam Demo Video.

Constant Force Balance Springs

Today’s window requirements demand quality and consistency. Springs need to pull their weight…and no less.

1/2" yellow hatted and 1/3" blue hatted constant force springs lifting weights. Constant Force Balance Springs today’s window requirements demand quality and consistency. Springs need to pull their weigh and no less.

Our AAMA-qualified springs do just that, no matter how high the rated load.

  • ½” Series: 3 lb. through 10 lb.
  • ¾” Series: 3 lb. through 13 lb.
  • ⅜” Egress Series: 4 lb. through 7 lb.
Constant Force Balance Spring Download .pdf
Constant Force Balance Spring

Information Sheet

Constant Force Balance Spring Download .pdf
Constant Force Balance Spring

1/2″ Spring Selection Guide

Constant Force Balance Spring Download .pdf
Constant Force Balance Spring

3/4″ Spring Selection Guide

Need Assistance? Consult our Technical Team.

Our Technical Team offers a depth of expertise to assist you with all parts of the process. We are ready to answer your questions in a timely manner and will help you define what you need. We produce custom springs for all purposes, and we are here to work with you on any of your customization needs.