Spirotop's low profile and high-compression valve combine to give you a leak-resistant, high point vent that fits just about anywhere. Moreover, Spirotop resists dirt particles and sudden pressure shocks, which can cause ordinary vents to leak. When filling or draining a system, venting high points, or eliminating air locks, the Spirotop automatic air vent is the only choice for those who want reliable, problem-free results every time. Unique valve mechanism is guaranteed not to leak and cannot be shut off. Standard thread for vent pipe connection or pressure testing. Specially constructed air chamber to protect the valve mechanism from dirt. Sufficient volume to handle pressure fluctuations. Solid brass construction for extended service life.