In-House Repair And Maintenance Of DOT4L Liquid Cylinders

These valuable assets can be costly if improperly diagnosed.

How to speed up the process of putting valuable assets, such as DOT4L liquid cylinders back into service is a problem that plagues many gas distributors. The difficulty or inability to properly diagnose a malfunctioning liquid cylinder is one of the primary reasons these valuable assets are not in the field, generating revenue. In many cases, only basic, inexpensive repairs or component adjustments or replacements are required in order to have a liquid cylinder properly functioning again. The key to making this happen is the ability to properly diagnose, identify and repair liquid cylinders efficiently and effectively.

liquid cylinder repair

The key to having liquid cylinders properly functioning is the ability to diagnose, identifty and repair them efficiently and effectively.

Vacuum Problem
Bad vacuum is the most common misdiagnosis of a DOT4L liquid cylinder. There are many simple malfunctions that can lead a distributor to believe that a liquid cylinder may have a bad vacuum or other significant problem, resulting in either a costly repair bill or the liquid cylinder being removed from service for an extended period of time, until a proper diagnosis can be made. Oftentimes, these assets unnecessarily sit idle and out of service for an indefinite period of time, when in many cases a simple, inexpensive repair is all that is required.

The first step in ruling out a vacuum problem is to check the vacuum integrity of the liquid cylinder. Traditional NER (Normal Evaporation Rate) testing requires the distributor to fill the liquid cylinder, record the weight of the product, wait  24 hours, record the weight of the product again, determine the amount of product loss after 24 hours, calculate that percentage and then compare it against the manufacturer’s published NER percentage. Many distributors do not have the time, tools or resources to effectively accomplish such testing. This testing can be simplified by using a vacuum meter, which is essentially a flowmeter specifically designed and calibrated for measuring and weighing product vapor (gas) escaping from the liquid cylinder’s vent valve and indicating “Poor or Failing,” “Good” or “Excellent” vacuum integrity. This process does not require a scale and can be done in a fraction of the time required for a traditional NER test.

Performance Issues
The top end components on a DOT4L liquid cylinder are relatively simplistic and, with a little bit of knowledge on their intended function, performance and design, performance issues can easily be identified, isolated and repaired. Many gas distributors already have employees with this knowledge; there are also classes available to distributors designed specifically to teach how to diagnose, identify and repair or replace the top end components. This information can be invaluable for a distributor in maintaining a liquid cylinder fleet.

Something as simple as a plumbing leak or bad relief valve can easily give a false indication of a potentially bad vacuum.

For example, something as simple as a plumbing leak or bad relief valve can give a false indication of a potentially bad vacuum. A liquid cylinder not building pressure may only have a bad relief valve or an improperly set pressure building regulator. An iced-up container may only have a pressure building valve that is not properly closed. A broken gas, vent or liquid valve may only need a simple rebuild kit.

In-house repairs can also be simplified by having the ability to test the performance of the individual top end components, such as relief valves, regulators, pressure gauges, etc. A simple pressure testing and resetting manifold can accomplish the majority of these tasks.

What does all of this mean to the average gas distributor? Liquid cylinders are valuable assets for generating revenue, but they can also be very costly to a gas distributor for a variety of reasons, if improperly diagnosed and not maintained. A malfunctioning liquid cylinder may not only be removed from the fleet and no longer be generating revenue, but it can also be very costly when a malfunction results in product credits, rush delivery charges to replace a malfunctioning container, unsatisfied customers and, worst of all, potentially investing in new liquid cylinders when the current assets could have been easily put back into the field and generating revenue, contributing directly to the bottom line.

Gases and Welding Distributors Association
Brent Lockhart Brent Lockhart is vice president of sales at Ratermann Manufacturing Inc., located in Livermore, California, and on the Web at