Q4 2008 / Avoid costly stumbling blocks when specifying specialty gas equipment
Frank Scornavacca
President
SGD, Inc.
frank@sgd.com
Ordering critical gas-handling equipment for a system or process your
company is assembling is never a seat-of-the-pants exercise. Proper
operation, profits, and safety are at stake with every buying decision
you make, and the path to doing it right the first time can be strewn
with stumbling blocks that are easily avoided.
Any system you build requires certain information to ensure that the right choice has been made for the application involved. Usually, the information you need is right at your finger tips, and it can be compiled by answering “Five Questions.” Even when you cannot answer these questions with certainty, you can usually depend on your supplier to lead you to the right answers.
The Proposition: Build a specialty gas panel that will be mounted in a gas cabinet.
The Approach: Design it and specify the equipment needed after you ask yourself the following “Five Questions” before you place that call or write a purchase order.
Question 1. Which gas or gases
are involved?
On the surface, this appears to be a very simple question, but very often it is a question that a caller cannot fully answer. In one instance, a caller stated: “I need a regulator for ammonia.” Our question: “Is it pure ammonia or a mixture with ammonia?” Caller’s response: “I don’t know, does it make a difference?”
The answer is clearly, “Yes!” Pure ammonia is a liquefied gas under its own vapor pressure of 114 psig at 70F, and would normally require a single-stage stainless steel regulator with an inlet pressure gauge of 400 psig or possibly no inlet pressure gauge. The pressure, however, does not vary as the gas is withdrawn until all of the liquid is vaporized. At that point, the pressure decreases rapidly.
With liquefied gases, it is best to monitor content by weight with a scale. If the gas in question is a mixture that contains ammonia; e.g., a 100 ppm ammonia in nitrogen calibration mixture, then the proper regulator could be a stainless steel, two-stage regulator with a 3,000 psig inlet pressure gauge.
Of course, you need to know the gas and its composition so that you can select the proper CGA connection for the regulator. In the case of ammonia, this is not easily determined. Depending on the gas supplier and the grade, the connection for pure ammonia may be any one of three CGA connectors: 240, 660, or 705. An ammonia mixture may require either a 660 or a 705. The end-user must supply you with the correct information about which CGA connection is needed to ensure that the regulator supplied can be connected to the cylinder received.
Question 2. What is the delivery pressure or the system operating pressure?
Once the pressure of the cylinder in “Question 1,” has been determined, the delivery pressure of the regulator must be determined. When Question 2 is posed, the response often is: “Whatever is standard” or “low.” To properly specify a regulator we need numbers, and only the customer can provide this information.
If we are trying to specify a purifier, filter, flow meter, or other device, we need to know the operating pressure to ensure that the rated working pressure of the unit is sufficient.
Question 3. What is the flow requirement?
This question often generates silence on the other end of the phone line. It is the hardest piece of information to obtain from a customer, but the answer is very necessary to ensure that the right equipment for the application is provided.
Answers like, “low” or “high” are just not sufficient. We do not need to know an exact number, but we need a good estimate. For example, if someone working in a laboratory states that the flow rate is low, the flow rates that come to mind are 100 to 1,000 cc per minute. However, if the call is from someone working in a petrochemical plant states that their flow rate is low, we would be inclined to think of flows ranging from one to 10 cubic feet per minute—or more.
Under normal cylinder applications, we can often estimate the flow rate with some empirical usage data from the customer. For high pressure gases, such as helium or nitrogen in 200 or 300 cubic foot cylinders, a good rule of thumb is that usage is equal to 10 cubic feet for every 100 psig drop in cylinder pressure over time; i.e., if the cylinder pressure drops 300 psi during an eight-hour shift, the estimated usage is 3.75 cubic feet per hour.
In the case of liquefied gases, using a simple cylinder scale, we can make a similar determination by monitoring the difference in weight over a period of time and then multiplying by the specific volume of the gas. Assume a cylinder of carbon dioxide as an example. The weight difference over an eight-hour period is 10 pounds, resulting in a flow of 1.25 pounds per hour. Multiplied by the specific volume of carbon dioxide (8.76 cubic feet per pound), the resultant flow rate of 10.95 cubic feet per hour is obtained.
A simple cylinder scale can help determine the flow rate from a liquefied gas cylinder.
Question 4. What are the gas sources?
This may appear to be an unimportant question, but we have often experienced situations in which the customer wants to order a manifold or changeover and expects a flow rate well in excess of the capacity of the containers that will be connected to the system. This is often the case when containers of liquid nitrogen are the source. These containers can provide up to 325 cubic feet per hour continuously, but if flows exceed this rate, the liquid gas cannot vaporize quickly enough to maintain the pressure. The result is that the pressure in the container will be reduced to a point at which it can no longer deliver the required flow. A similar situation exists with high-pressure cylinders when a customer expects to deliver 5,000 cubic feet per hour from a single 300-cubic foot cylinder without realizing that even if he could maintain that flow, the cylinder would only last 3.6 minutes.
Question 5. What is the application?
This could very well be “Question 1,” but often the conversation starts with “I need a regulator,” and finally proceeds to a detailed discussion of the full application to ensure that all of the pieces work together. Also, one of the first questions has to be: “Is it a high purity application?” A “Yes” answer dictates specific equipment parameters, such as the requirement for a high-purity regulator with a stainless steel diaphragm. However, every component in the system must be considered in the same light.
Summary
While the five questions may appear to be tedious, it is best to secure the complete information up front. This will ensure that the user ends up with the right equipment for the application; thus, eliminating customer frustration and the need to make multiple shipments, then deal with the question of returns.
Frank Scornavacca
Frank Scornavacca is president of SGD, Inc., a single-source, full-line wholesale specialty gas distributor with a unique support program. He can be reached at:
frank@sgd.com
Any system you build requires certain information to ensure that the right choice has been made for the application involved. Usually, the information you need is right at your finger tips, and it can be compiled by answering “Five Questions.” Even when you cannot answer these questions with certainty, you can usually depend on your supplier to lead you to the right answers.
The Proposition: Build a specialty gas panel that will be mounted in a gas cabinet.
The Approach: Design it and specify the equipment needed after you ask yourself the following “Five Questions” before you place that call or write a purchase order.
Figure 1. Special gas panel mounted in a gas cabinet as developed from a “five-question” discussion.
On the surface, this appears to be a very simple question, but very often it is a question that a caller cannot fully answer. In one instance, a caller stated: “I need a regulator for ammonia.” Our question: “Is it pure ammonia or a mixture with ammonia?” Caller’s response: “I don’t know, does it make a difference?”
The answer is clearly, “Yes!” Pure ammonia is a liquefied gas under its own vapor pressure of 114 psig at 70F, and would normally require a single-stage stainless steel regulator with an inlet pressure gauge of 400 psig or possibly no inlet pressure gauge. The pressure, however, does not vary as the gas is withdrawn until all of the liquid is vaporized. At that point, the pressure decreases rapidly.
With liquefied gases, it is best to monitor content by weight with a scale. If the gas in question is a mixture that contains ammonia; e.g., a 100 ppm ammonia in nitrogen calibration mixture, then the proper regulator could be a stainless steel, two-stage regulator with a 3,000 psig inlet pressure gauge.
Of course, you need to know the gas and its composition so that you can select the proper CGA connection for the regulator. In the case of ammonia, this is not easily determined. Depending on the gas supplier and the grade, the connection for pure ammonia may be any one of three CGA connectors: 240, 660, or 705. An ammonia mixture may require either a 660 or a 705. The end-user must supply you with the correct information about which CGA connection is needed to ensure that the regulator supplied can be connected to the cylinder received.
Question 2. What is the delivery pressure or the system operating pressure?
Once the pressure of the cylinder in “Question 1,” has been determined, the delivery pressure of the regulator must be determined. When Question 2 is posed, the response often is: “Whatever is standard” or “low.” To properly specify a regulator we need numbers, and only the customer can provide this information.
If we are trying to specify a purifier, filter, flow meter, or other device, we need to know the operating pressure to ensure that the rated working pressure of the unit is sufficient.
Question 3. What is the flow requirement?
This question often generates silence on the other end of the phone line. It is the hardest piece of information to obtain from a customer, but the answer is very necessary to ensure that the right equipment for the application is provided.
Answers like, “low” or “high” are just not sufficient. We do not need to know an exact number, but we need a good estimate. For example, if someone working in a laboratory states that the flow rate is low, the flow rates that come to mind are 100 to 1,000 cc per minute. However, if the call is from someone working in a petrochemical plant states that their flow rate is low, we would be inclined to think of flows ranging from one to 10 cubic feet per minute—or more.
Under normal cylinder applications, we can often estimate the flow rate with some empirical usage data from the customer. For high pressure gases, such as helium or nitrogen in 200 or 300 cubic foot cylinders, a good rule of thumb is that usage is equal to 10 cubic feet for every 100 psig drop in cylinder pressure over time; i.e., if the cylinder pressure drops 300 psi during an eight-hour shift, the estimated usage is 3.75 cubic feet per hour.
In the case of liquefied gases, using a simple cylinder scale, we can make a similar determination by monitoring the difference in weight over a period of time and then multiplying by the specific volume of the gas. Assume a cylinder of carbon dioxide as an example. The weight difference over an eight-hour period is 10 pounds, resulting in a flow of 1.25 pounds per hour. Multiplied by the specific volume of carbon dioxide (8.76 cubic feet per pound), the resultant flow rate of 10.95 cubic feet per hour is obtained.
A simple cylinder scale can help determine the flow rate from a liquefied gas cylinder.
Question 4. What are the gas sources?
This may appear to be an unimportant question, but we have often experienced situations in which the customer wants to order a manifold or changeover and expects a flow rate well in excess of the capacity of the containers that will be connected to the system. This is often the case when containers of liquid nitrogen are the source. These containers can provide up to 325 cubic feet per hour continuously, but if flows exceed this rate, the liquid gas cannot vaporize quickly enough to maintain the pressure. The result is that the pressure in the container will be reduced to a point at which it can no longer deliver the required flow. A similar situation exists with high-pressure cylinders when a customer expects to deliver 5,000 cubic feet per hour from a single 300-cubic foot cylinder without realizing that even if he could maintain that flow, the cylinder would only last 3.6 minutes.
Question 5. What is the application?
This could very well be “Question 1,” but often the conversation starts with “I need a regulator,” and finally proceeds to a detailed discussion of the full application to ensure that all of the pieces work together. Also, one of the first questions has to be: “Is it a high purity application?” A “Yes” answer dictates specific equipment parameters, such as the requirement for a high-purity regulator with a stainless steel diaphragm. However, every component in the system must be considered in the same light.
Summary
While the five questions may appear to be tedious, it is best to secure the complete information up front. This will ensure that the user ends up with the right equipment for the application; thus, eliminating customer frustration and the need to make multiple shipments, then deal with the question of returns.
Frank Scornavacca
Frank Scornavacca is president of SGD, Inc., a single-source, full-line wholesale specialty gas distributor with a unique support program. He can be reached at:
frank@sgd.com
