Zilmet, ZEP-1, Thermal Stainless Steel Expansion Tank and Shock Arrester

The Zilmet ZEP-1 is a compact stainless steel thermal expansion tank and shock arrester designed for tankless and point-of-use water heaters with 2 gallons or less of total water volume. It manages hot water temperature-related expansion in a closed plumbing and water heating system, helps support stable water pressure, and features a 1/2 inch NPT connection. NSF 61 certified.

The Zilmet ZEP-1 is an essential component for homeowners, contractors, and property managers using or installing tankless and point-of-use water heaters where tight spaces and closed plumbing loops require reliable thermal expansion protection, and where installation decisions may depend on available experience. Built for systems with 2 gallons or less of total water volume, it is made from 304 stainless steel for corrosion resistance and long-term durability, especially where backflow preventers or check valves can create the closed conditions that cause thermal expansion. Here you'll find the key features, specifications, pressure ratings, and use cases that matter when comparing or selecting a compact expansion tank for leak prevention, water hammer reduction, and longer heater life.

A diaphragm membrane separates water and air, absorbing added volume by compressing the air cushion as hot water temperature rises. As water cools, some water can be sucked back toward the line side while the air cushion helps balance pressure.

• Thermal expansion tank and shock arrester for tankless and point-of-use water heaters
• Designed for systems with 2 gallons or less of total water volume
• Compact size helps fit tight installation spaces
• Stainless steel construction
• 1/2 inch NPT connection
• NSF 61 certified
• Model ZEP-1

Thermal Expansion Tank Specifications

• Material: 304 Stainless Steel
• Capacity: 0.05 gallons
• Size: 3.2" x 2.8"
• Discharge Connection: 1/2" NPT
• Maximum Working Pressure: 150 PSIG
• Factory Precharge: 50 PSIG (adjustable)
• Shipping Weight: 1 lb
• Universal Product Code: 8019855054139
• Drawdown @ 30/50 PSI: 0.03 gallons
• Drawdown @ 40/60 PSI: 0.03 gallons

Benefits of Thermal Expansion Control

• Helps prevent leaks and structural damage caused by pressure spikes in closed systems from thermal expansion effects
• Assists in reducing pressure fluctuations and water hammer conditions before they fall to inconsistent levels across the system for more consistent water flow and water pressure
• Compact size allows installation in limited spaces
• Durable stainless steel construction for long service life; expansion tanks typically last five to ten years with proper system conditions and periodic checks
• Suitable for tankless and point-of-use water heater applications; while most homes frequently need a 2-5 gallon expansion tank, this model is designed for systems with 2 gallons or less
• NSF 61 certified for potable water system use