General gas related questions  [ Return to  FAQ  ]

1- What is the difference between certified and primary mix?

The most significant difference between the two mixture grades lies with the level of certification that is offered. Traditionally, primary mixtures are also known as gravimetric mixtures and are filled by weight using high-load, high-sensitivity balances. Each component is weighed in and verified. The mixture concentration is confirmed by gas chromatography and then the gravimetric result (4 significant figures) is offered to the customer, whereas the analytical results (3 significant figures) are offered in the case of a certified mixture.

2- What is the difference between a needle valve and diaphragm valve?

A needle valve is used when the application requires fine-tuning in terms of a flow from a regulator or other source of supply. With each turn of the regulating knob, gas is marginally allowed to flow. In the case of a diaphragm valve, gas flow is abrupt open or closed.

3- Why a specialty gas versus an industrial?

It all depends on the application and needs pf the customer. Essentially, a specialty gas grade comes with a level of confidence in the purity of the gas held within the cylinder and the level of impurities that may affect a customer’s process. Whenever discussing an application, always refer to the specialty gas catalogue and inquire what impurities may affect their process.

4- Does Air Liquide sell nitrogen (or argon) 5.0/4.8?

The notation 5.0 or 4.8 refers to the purity level of a pure gas. As an example, nitrogen ALPHA 1 is certified to be 99.999% pure, 5 nines, hence 5.0, while Nitrogen HP+ is certified to be 99.998% pure, 4 nines and an 8, hence 4.8. It remains important to inquire if any particular impurities affect the customer’s process.

5- What does PPM mean in terms of impurity?

Parts per million (PPM) is a measure of nominal concentration of any fluid or gas. Similar to percent, which is based on a 100 unit basis (10% is 10 parts per 100), 100 PPM refers to 100 parts per 1 000 000 (1 million). Therefore, 100 PPM is equivalent to 0.01% of X in Y, or CO2 in N2.

6- What is hydrocarbon free?

A hydrocarbon free gas is one in which the gas is certified to have a guaranteed level of hydrocarbon impurities, measured as methane. For example, hydrocarbon free nitrogen is under 0.5 PPM Total HydroCarbon (THC).

7- Is Alpha 1 the same as UHP?

The Alpha 1 grade is Air Liquide's simplification of gas grades in order to meet 99% of the gas purity requirements of the Laboratory & Analytical market needs. The Alpha 1 product line offers 5.0 purity for all standard high purity gases such as nitrogen, helium and argon.

8- What is an RPV valve? Scandina cap?

The Residual Pressure Valve (RPV) is an innovation added to the Alpha line of gases. The valve is designed to maintain a residual pressure within the cylinder so as to maintain the integrity and purity of the gas. The Scandina cap is Air Liquide’s response to the nagging issue of cylinder caps difficult to remove and possibly resulting in injury when customers force the cap. With the open-concept protection, customer is assured of the same level of safety as with a traditional cap all the while having direct access to the valve outlet.

9- Why use aluminum cylinders and not steel cylinders?

Aluminum cylinders are used in order to assure stability of low concentration reactive gas mixtures during and after the fabrication process. Studies have shown that reactive species such as hydrogen sulfide, sulfur dioxide or chlorine are best maintained within an aluminum cylinder. The most prominent factor is the difference in wall surface of an aluminum cylinder versus that of a steel cylinder. Aluminum offers fewer sites in which impurities may reside and react with the hydrogen sulfide such as humidity or oxygen.

10-What is difference between preparation tolerance and analytical accuracy?

Preparation tolerance refers to the amount of latitude permitted during the manufacture of a mixture so as to consider it acceptable and not be rejected. A mixture of 10% carbon dioxide in nitrogen can be considered within tolerances if its final concentration falls between 9.5% and 10.5% CO2. Analytical accuracy refers to how close the analytical result is to the “true” value within the cylinder. Specialty gas offers a standard analytical accuracy of 2% relative or 0.02% absolute. In the example above, if the analytical value has been determined to be 10.3%, the true value of the concentration is believed to be within 10.1% and 10.5%.

11-What is a gravimetric mix?

A gravimetric mix refers to a mixture in which all gas components are added by weight using high-load, high sensitivity balances using the primary method of measure of mass.

12-What is Calgaz and when should it be used?

CALGAZ is the Air Liquide division, which supplies calibration mixtures and pure gases destined for the analyzer & equipment sector. Cylinders are lightweight and compact and are designed for easy transport and use in confined areas where a traditional cylinder is either too large or too heavy to be used.

13-What is the difference between a single stage & double stage regulator?

The principle difference between a single & double stage regulator is in the ability of a double stage regulator to provide a constant supply of gas to the application such as gas chromatography. While both regulate and decrease gas pressure the single stage does it in one step and the 2-stage regulator does it in 2 stages of regulation.

14-What is the difference between a certificate of analysis and certificate of conformity?

A certificate of conformity is a document, which simply reaffirms the guaranteed purity of a gas as it relates to the grade and batch analysis. There has been no SPECIFIC analysis to a cylinder other than the witness cylinder used to qualify the batch. A certificate of analysis (CofA or COA) refers to a specific analysis in regards to a gas grade for a particular cylinder or group of cylinders. That is, each cylinder, referred to on the certificate has been individually analyzed.

15-When should a stainless steel a regulator be used?

Stainless steel regulator is required when issues of material compatibility are to be considered and when brass is known to be unacceptable for a particular pure gas or mixture in terms of reactivity and gas stability.

16-Why does it take so long to produce & deliver toxic mixtures?

Toxic or reactive gas mixtures are made in accordance to procedures and methodology that will assure mixture stability and safety throughout the manufacturing process. Once prepared, the mixture requires to be analyzed several times over a period of time (days) in order to certify the stability of the mixture and guarantee it throughout the documented shelf life period. In addition, product and cylinder availability play a factor, level of complexity as well as plant load, which collectively adds to the delivery period.

17-What is a security mixture?

A security mixture is one that contains both flammable and oxidizing gases in the same cylinder. In order to be produced a security authorization is required from Air Liquide Paris. As such, the mixture is prepared under specific instructions, on a special ramp and produced one cylinder at a time in order to assure the highest consideration towards safety. An example is be 500 PPM hydrogen in Air.

18-What services do Specialty gases supply?

Some of the services provided under the specialty gas product line are; 1- Safety training 2- Safety audits 3- Analytical services 4- Cylinder disposal 5- Installation of equipment or piping

19-Which gases can be generated on-site?

Only three gases can be manufactured on-site within the specialty gas product –line, they are: nitrogen, hydrogen and air. For more complete information, communicate with your local specialty gas representative or market specialist.