This specific 2" clear PVC check valve is a common part used across the hot tub industry by a wide array of manufacturers, making a comprehensive list difficult. Instead, major manufacturers whose spas commonly incorporate generic plumbing parts like this include:
Jacuzzi and Sundance Spas: These manufacturers, among others, use standard 2-inch plumbing components and related check valves in various models.
Master Spas: Frequently uses widely available plumbing parts, including 2-inch check valves.
Hot Spring Spas and Caldera Spas: As part of the Watkins Wellness group, they use industry-standard parts in their diverse lines.
Arctic Spas: Known for robust systems, they incorporate common flow-control parts like this check valve.
Dimension One Spas: Utilizes standard 2-inch plumbing components in their spa lines.
Marquis Spas: Employs common check valves for backflow prevention in their circulation and jet pump lines.