Models 7725, 7725i, 9725, and 9725i Analytical Injectors
The 316 stainless steel models 7725 and 7725i, and PEEK models 9725 and 9725i are Rheodyne's most advanced manual sample injectors for  analytical HPLC. These dependable injectors are the newer versions of the classic Rheodyne injector 7125 (page 7). New specialized features include:
• The Rheodyne patented Make-Before-Break (MBB ™ ) architecture allows continuous flow between LOAD and INJECT positions which greatly reduces transient pressure shocks that disrupts your system. See Figure 3.
• Wide, 30° port angles offer easier access to fittings using the Rheodyne Wrench (Part # 6810 on page 20).
• Front-end pressure screw makes it easy to adjust and maintain pressure.
• Capability of a reproducible 2 µL sample injection with a 2 µL internal sample loop.
• A built-in position sensing switch ("i" versions) provides the chromatograph with a reproducible start signal.
Figure 3 illustrates the MBB valve design. In the LOAD position, mobile phase flow from pump port to column port travels through both the rotor seal groove and the MBB passage (Position A). As the rotor seal grooves rotate to change from LOAD to INJECT, there is continuous mobile phase flow through both one rotor seal groove and the MBB passage (Position B) until the rotation stops and both rotor seal grooves are connected by the loop. Sample flow begins through the loop to the column just as all flow stops through the MBB passage (Position C). Sample flow never enters the MBB passage.