Wayne Lamb, Managing Director at Cadway Projects, has over 25 years experience in the fuel industry. He recently wrote an article for the Australasian Convenience and Petroleum Marketers Association (ACAPMA) magazine, which discusses the advantages and disadvantages of Suction and Pressure fuel pump systems for underground tanks. You can read the full article here:
Fuel Pumping Systems for Underground Tanks – Pressure or Suction
There are 2 methods of delivering your products from the tanks to the customer, these being either suction or pressure pumping system. As with most things, there are advantages and disadvantages with both methods.
Suction Product Pumping Systems
This is the older technology where pumping force is provided by a pump in the bowser located on the forecourt. The pump ‘sucks’ the fuel up from the tank. Negative pressure is created in the product line and the fuel is ‘pulled’ up from the tank in the same way that sucking on a straw to drink your soft drink (or stronger..?) works.
- If a pump is out of service all products are still available from other dispensers on site.
- More simply integrated into older facilities where suction systems are employed.
- Simpler electrical installation as there are no power requirements at the tank end of the system.
- Max of 3m height that a suction pump can pull the fuel up from the bottom of the tank before a risk of vaporisation and cavitation results.
- Restriction the size and burial depth of the storage tanks. A modern, large diameter tanks (3m to 3.5m diameter) cannot be used with a suction system which limits the volume of storage.
- Hot summer’s days and low product levels in the tank increase the risk of vaporisation of the fuel.
- Long runs of product delivery pipework reduce the effectiveness and efficiency of suction pumps.
- The suction pumps on the forecourt can be noisy and perceived negatively by your customers.
- Generally, more underground pipework is needed for a suction system. For 4 dispensers with 4 products each there are 16 separate pipes running from the tanks.
- Suction pump dispensers are more expensive to purchase than pressure system dispensers.
- For a busy site, suction systems are usually more expensive to run.
- No active method of line leak detection is available for suction system product pipework.
Pressure Product Pumping Systems
About 20 years ago this new technology came to Australia which places the pump in the bottom of the tank and ‘pushes’ the product through the pipe to the dispenser which is essentially only a meter, a display, a hose and nozzle in an otherwise fairly empty cabinet. The head unit of the pump is housed below driveway level in a tank turret directly above the top of the tank and is accessible via a driveway cover.
- It eliminates the risk of vaporisation and therefore cavitation in the system.
- It is not restricted in how far or how high the product can be pumped (within reason).
- Larger diameter tanks can be used and less product pipework is necessary because the dispensers are installed in series on a common pipeline for each product. So 4 dispensers with 4 products each only need 4 product pipelines from the tanks.
- Dispensers run quietly on the forecourt.
- Dispensers are cheaper and the reduced pipework lengths go towards balancing the cost of STPs and turrets, driveway covers and additional electrical services.
- Active mechanical and electronic line leak detection can be installed.
- Can provide flexibility in future expansion of the forecourt with additional dispensing locations.
- Runs a single pump for multiple dispensers so overall running costs can be less.
- If a pump is out of service then often that product is unavailable at all the dispensers. It has been my experience, however, that the modern pumps are very reliable and it is quite reasonable to expect to get many years of service without a problem.
- A more complicated design is required and a more highly skilled installation contractor needed to install it.
There are cases where a new pressure system can be retro-fitted onto an existing underground tank system which previously ran a suction system. As long as there is a minimum of 750mm of cover to the top of the tank, a pressure system complete with tank turret and driveway covers etc is likely possible to install. This will deliver all the advantages of a pressure system but, should the existing tanks be steel, it does not remove the inherent risks associated with underground steel tanks as discussed in our previous article.
I hope this has been a useful look at some of the factors to consider when next you need to invest in a product pumping system whether it is a new installation or upgrading an existing one. Whether to go with the more modern pressure system or continue with a suction system will depend on what value you place on the various advantages and disadvantages listed here. From an environmental standpoint, however, there can be little doubt that the pressure system offers a superior outcome, greater levels of leak detection and therefore greater peace of mind in the long term.