LoPro™ Two-Stage Poppet Valves To achieve a soft pumpdown of your vacuum system with limited space conditions, we recommend our HPS® LoPro Two-Stage Valve. A low-profile isolation valve with an integrated small bypass valve, the LoPro Two-Stage significantly simplifies system setup and reduces costs. The LoPro Two-Stage Valve is best suited for high vacuum applications, specifically semiconductor or optical processing for which a cleaner environment is necessary. With the integrated slow pumpdown feature, turbulent flow is diminished preventing contamination buildup and damage to your product.