What is a Medical Gas Manifold?
Unlike Medical Air Compressors and Vacuum Pumps that generate gas on-site, many gases used in healthcare settings are delivered to the facility in different types of containers and use manifolds to distribute into the rooms. Gases that can be delivered:
The 2021 edition of the NFPA99 has the most recent developments in medical equipment and processes as well as new methods to reduce fire, explosion, and electrical hazards.
What Containers are used with Manifolds?
Bulk tanks and micro-bulk tanks are gas containers that get refilled on-site. These are used for large applications and require additional equipment. Sometimes, these are collectively called a tank farm and the pad – which allows access for a truck with cryogenic gas to pull in and fill the tanks.
Liquid Dewars and high-pressure cylinders are the types of gas containers that are delivered and replaced when empty. For example, there is an “H-type” high pressure cylinder, which is primarily hooked up to a high-pressure manifold in the healthcare setting. These are very common for ambulatory surgery centers and small outpatient facilities, most of the gases listed above outside of oxygen, still use this type.
High Pressure and Liquid Medical Gas Manifold Installation
Discussing high pressure and liquid medical gas manifolds located indoors, the number one aspect is that it has to be a separate secured room with one hour fire rating used for no other purpose. Your manifold room can only have the manifolds and the container that is being replaced. You can store and keep connected what you’re actually using.
For example, if you have Dewars, you are only able to store Dewars, and then your high-pressure cylinders (H tanks) can go in there. Sometimes people put the vacuum pump and the oxygen manifold in the same room – that is not allowed and very expensive change order. Remember, your manifolds must be in a room all by themselves and be properly labeled.
Although this blog discusses the most common practices, Pattons Medical advises you to always work with your local municipality and local verifier to ensure that your design complies with your interpretation of whichever code they’re working on. Additionally, please note that any electrical devices in this room must be situated above five feet, and relief valves must be installed with copper piping that extends outside the room. The discharge should be turned down and screened for safety. Another important consideration is having a source valve located near the manifold.
When it comes to the insulation of the room, there are several other factors to take into account. Firstly, the temperature inside the room should not exceed 125 degrees. Additionally, ventilation must be carefully planned and implemented to ensure optimal conditions. You are able to naturally ventilate the room if your total gas falls below 3000 cubic feet. You can access gas volume charts on the Pattons Medical website.
Reference NFPA 99 5.1.3.3.2 (1-9) for design and construction details for locations of central supply systems and storage of positive pressure gases.
Indoor rooms can be heated by indirect means using steam or hot water if needed. The common rule of thumb for your liquid containers, your Dewars, is depending on the gas, it could be between 12 and 16 H cylinders. You will know where you are in that 3000 cubic feet threshold by the math and whether you want to do the mechanical versus the natural.
How do Medical Gas Manifolds Work?
With medical gas manifolds, you will have two banks; the primary and the secondary, and they are required to be equal. In regards to space, the primary bank is the one currently supplying the gas, and then the secondary bank will be ready when the primary is depleted. The manifold is required to be fully automatic. Referring to the NFPA applications, the switchover must occur within the manifold, semi-automatic.
Discussing the manifold and the header bars, the header bars will need to be equipped with high-pressure shutoff valves outside the cabinet to allow for emergency isolation. You also will need to have integral check valves for each station. The header bar is going to be CGA gas specific. This means your H cylinder (your Dewar), has a certain threaded connection – similar to the header bar. The goal is to prevent a nitrogen, H cylinder from being hooked up to an oxygen manifold. With the CGA fittings, the manifold is equipped with pressure transduced – which will send information to the main circuit board for a remote signal. This is how it will talk to your master alarms. Since you will need to place this outdoors, the NEMA four gives you some weatherproofing. You will need to make it a NEMA four cabinet if you are going to do it outside. Pattons Medical recommends putting a cover or shelter over it.
What’s Inside a HP Manifold?
The manifold is going to come equipped with a three-quarter inch shutoff valve, which makes up a manifold for high pressure. At the bottom of the diagram, is the pressure transducers that are telling you what pressure is happening in each side, your left and right bank, and your primary and secondary. Then, we go into the left and right bank dome regulators. The important part about using the dome biased regulators is that it’s what holds the pressure to allow the whole thing to work off pressure differential.
Above those, are the first line regulators. Then, the bank gauges at the top tell you what's going on in these headers. After that, there’s the pilot regulator, which is feeding pressure into the dome bias, so your dome bias regulator is about 25 – 30 PSI higher than the one that it’s currently feeding.
When a facility gets gas delivered to their site, they are paying for gas at a certain purity, when the gas gets delivered on site, there is no way to make it pure. Manifolds can affect the purity of the gas, so if you’re not using high quality regulators that are made for NFPA applications, then there is potential through the regulator to introduce some impurities into the gas as it flows through the manifold. The left bank is feeding the facility, but when it drops to 250 PSI, it is no longer satisfying the dome biased, then it’ll switch to the secondary bank.
In our second “true” line regulators, which is where it gets put it into the building. All of these regulators are preset at the factory depending on the gas. Discussing the delivery pressure being different depending on the gas, your bank of H cylinders is going to have different, depending on the gas. For example, a bank of oxygen, H cylinders track about 2200 PSI, but a bank of nitrous oxide cylinders only track about 750 PSI. So, these regulators all come preset from the factory gas specific. Then you go through the line regulator. The image shows both regulators being open, but when you are truly feeding the facility, only one regulator will be open.
The manual purge valve will test for purity. The pressure relief valve is there to let you know if something is wrong and it will relieve off. When you are determining the flow through the manifold, some spec sheets give you the flow with both your left line regulator and your right line regulator being open, flowing through both, but this is not accurate for an NFPA application. For maintenance, the left line regulator will be manually turned off and then the right line regulator will need to be turned on. That is strictly to keep the wear and tear equal within the manifold.
There are manifolds on the market that use what’s called a “switching,” which is when it switches to where the pressure is after one side no longer has any pressure. The issue with this is that they leak and cause a waste of gas. The other caveat is that they fail frequently in the middle, so they haven’t closed the left bank but they opened the right bank. So, you end up using both banks at once with no warning.
Heaters
CO2 and nitrous are two gases that can potentially freeze up a manifold. This is caused by a pressure drop and flow across the regulators in the orifice in the manifold. If you’re going to use a manifold with a shuttle valve, you must have a heater for CO2 and nitrous oxide because they leak. Then, you will be left with a slow flow the eventually freezes, so you’ll need to use a heater. We have a high flow dome bias regulator in our manifold, our specification sheets do not specify a heater with a Pattons Medical manifold. It isn’t needed because Pattons Medical picked a regulator that would give us high flow. Pattons Medical also wanted to make it so that heaters weren’t needed because they add to the room which causes another fail point. The heaters basically work by switching on when the room temperature drops below 75 degrees.
Liquid x Liquid Manifold
In larger facilities, the number of high-pressure cylinders required to meet the demand can become very high resulting in a huge space requirement and a very labor-intensive change out. In those instances, cryogenic containers become advantageous. If using cryogenic containers, there are options pertaining to the primary and secondary banks. If using a liquid manifold, a HP reserve manifold is required as back-up.
IntelliSwitch Manifold
The IntelliSwitch manifold is the product we will need to use if you are using a liquid-by-liquid application or high pressure. One of the unique features of the IntelliSwitch manifold is the flexibility.
When you push the button on the front, it allows you to identify what is being connected to this manifold. What this manifold's able to do is when you tell it what is connecting to it, it will understand what pressure is supposed to see based on the containers being attached.
When you liquefy the gas in the container, it introduces some challenges with the gas being in a cryogenic state. IntelliSwitch is able to address some of those challenges. One of the first features is the economizer function. For this example, we will say, that this bank is feeding the facility. When this bank is feeding the facility, this container is generating head pressure because the gas does not want to be in a liquid state. When it generates too much head pressure, that's when you're going to pop your pressure relief valve to protect the container. In a traditional liquid by liquid manifold, it blows off into the room.
The IntelliSwitch is able to monitor the pressure on the bank, feeding the facility. Still, it’s also monitoring the pressure of the bank, not feeding the facility when it starts to register, that the head pressure is getting to. The economizer feature just bleeds some of that gas off so that it's able to be used downstream and you don't waste it. All of this happens in reverse with the lookback feature.
The lookback feature will do a soft switchover, and start drawing some of the gas from this bank, but then it keeps looking back. When this generates enough head pressure, it uses it. If it notices that there is no type of gas or that its completely empty, it’ll switch to the alternative. So instead of wasting 30% of gas in the container, only 5% will be wasted. The majority of verifiers say that this is a safer product because you are constantly getting readouts from both, meaning you know exactly what the pressure is.
Working with a verifier is essential. Take into consideration whether they are truly third parties or selling products as well.
Alarms
For the manifold, there are local and master alarms. The local alarms are physically on the cabinet and are going to have either green or red lights. These lights will be next to a few phrases; ready, in-use, and replace.
For reference, you should have two green lights for ready, which means you now have a demand. For this example, let’s say this is your primary bank. When it’s depleted, the red light will be next to “replace” and the green light will be next to “ready” and “in-use.”
At your master alarm, you have a low-pressure line, high-pressure line, and reserve in use. They are actually being read by the main line pressure switch downstream of the source valve, but then you have your changeover alarm. Similarly to the local alarm, if the red light for “replace,” it is telling you to change over. You will need to address getting the bank changed out within a specified timeframe.
For liquid by liquid, we have those same three alarm points at the master, but we also have to have two more points at the master alarm, called reserve in use. As mentioned, for liquid-by-liquid applications, you have your two cryogenics and your high pressure. If your cryogenic containers have both failed, we will take off our “reserve-in-use” for the high-pressure reserves. The reserve manifold will trigger an alarm at the master.
