Difference Between CGA 555 and CGA 510

At High Precision Gas, we value our customers and strive to consistently meet and exceed their expectations. With that said, we utilize CGA 555 valves in our LPG cylinders for liquid-to-liquid service to ensure Compressed Gas Association (CGA) and National Fire Protection Association (NFPA) compliance, safety, and ease of use.

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CGA 555 Valve Features include:

  • Excess flow (ball) check valve limits flow in case of line breaks or accidental disconnects
  • Fixed level vent valve
  • Full-length liquid withdrawal tube
  • Pressure relief valve
  • Male thread is easier to detect any minor damage versus female thread.
CGA 555 Valve Drawing




The usage of hydrocarbon falls into two different applications:

1. Liquid-to-Gas (Vapor).

CGA 510 valve is specified valve outlet connection for gas (vapor) withdrawal. CGA 510 valve helps to ensure that the user does not unexpectedly get liquid product, which can create operational and safety concerns such as a more intense flame.

2. Liquid-to-Liquid

CGA 555 valve is specified valve outlet connection for liquid withdrawal. This is used because liquid product provides a greater Btu than gas (vapor) and acts as a solvent for extraction processes.

In order to prevent the adverse effects, one need to use the right valve according to the usage of hydrocarbon.

Why CGA 555 (and not CGA 510) when used in liquid-to-liquid butane/propane service?

1. CGA recommends to use CGA 555 in liquid-to liquid application to prevent pressure change that leads to vapor leaks.


2. NFPA 58 Liquified Petroleum Gas Code requires CGA 555 outlet and internal excess-flow valve for use in liquid service for capacity ≤ 420 lb propane capacity.

*source: NFPA 58 2017 Table*

3. The CGA 510 is the same fitting used in other gas applications (e.g., barbecue grills, gas stoves, outdoor gas heater), and therefore a CGA 510 with a liquid withdrawal tube attached can be easily mistaken and connected to a gas application. This can lead to a very dangerous scenario.

4. Well known valve OEMs (i.e., Rotarex, Rego, Sherwood, Marshall Excelsior) do not (and will not) sell a CGA 510 with a liquid withdrawal tube. Any CGA 510 with a liquid withdrawal tube is modified without the express consent of the valve OEM, and most have been discovered to not have an internal excess-flow provision installed.