Operational Costs for Vacuum Sewer Systems

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How much does it cost to operate and maintain your vacuum sewer system? Is that high and what is normal? Lets also talk about the best way to reduce your maintenance costs.

Critical Factors

Flovac’s operations group has completed audits of systems in many locations and through our benchmarking process we have determined a number of common factors involved.

Before we dig deeper there are two important statements we can make.

  1. You need to know how much your vacuum systems costs to operate. Most utilities, do not know. Once you understand what the main costs are, you can do something about them
  2. All systems which have monitoring systems installed have significantly lower operational costs as well as reduced risks.

The overall cost varies, smaller versus larger, country to country, so its probably best to focus on what makes up the cost. Try and find what was in the whole of life costs when this system was first being suggested. How accurate was that. If it is different, why is it different and if more expensive, what can be done about it.

Vacuum systems should always be cheaper to operate than a low pressure pump system and in a similar difficult location should have cheaper operations costs than a gravity system with multiple pump stations.

Cost Breakdown

  1. Energy Costs (30{f2ac4d1e1d40dc2e2d9280a1dfa90d854b2d8c80eba743affa37fc4ce2e16def}). For many utilities this is one of the easiest things to focus on and also easiest to get accurate data on.  It could be that your pumps are just old and it’s time for a rebuild/service or replacement. With vacuum systems, energy costs are highly correlated with the air/liquid ratio of the system. That’s our first design principal and our first operational health check. Air transports the sewage to the station. The amount of air is measured by the vacuum pump run times and the size of the pumps. If there is too much air, either due to leaks in the system, old valves or badly tuned valves then your vacuum pumps will run longer than needed. In most systems vacuum pumps should run approximately 6 hours per day. Sewage pump run times are determined by the amount of sewage in the system. If you have infiltration or a user dumping in more than they should, then your pump run time will increase. In most vacuum systems the sewage pumps should run about 2-3 hours per day. You need to check what the optimal air to liquid ratio is for your system. When it is at its optimal level your energy costs should be at their lowest possible point.
  2. Consumables (20{f2ac4d1e1d40dc2e2d9280a1dfa90d854b2d8c80eba743affa37fc4ce2e16def}) In vacuum systems consumables can either be related to parts for the vacuum valves and controllers, or related to pump station equipment. This is different to long term capital replacements, pump and valve replacements, this is covering annual spending on oil and filters and valve/controller parts. In our experience of sales of parts to systems, valve and controller parts should only be required every ten years. It is highly unusual for sales to be any more frequent than this. In most pump stations the main cost is oil and filters for rotary vane vacuum pumps. Liquid ring pumps and claw vacuum pumps require a lot less maintenance but might not handle the required duty for your system. The best way to reduce your oil costs is to reduce the run time on your pumps. See the above section on energy costs. If you are watching the air/liquid ratio and keeping your pump run times at optimal levels then your oil requirements will be minimal.
  3. Preventative Maintenance (30{f2ac4d1e1d40dc2e2d9280a1dfa90d854b2d8c80eba743affa37fc4ce2e16def}) A number of systems do no preventative maintenance at all and so this 30{f2ac4d1e1d40dc2e2d9280a1dfa90d854b2d8c80eba743affa37fc4ce2e16def} cost will be lumped in with call-outs. We would tend to visit each pit once a year to check the pit condition, valve condition and controller timing. At every ten years we replace the required parts in the valve and controller. With monitoring a lot of our preventative maintenance time is spent at the computer. Analysing data to show infiltration, air/liquid ratio, changes to end of line pressure, failing components and remotely adjusting the timing of certain controllers to take into account seasonal flows as required.
  4. Call-Outs (20{f2ac4d1e1d40dc2e2d9280a1dfa90d854b2d8c80eba743affa37fc4ce2e16def}) If preventative maintenance is done correctly then this number should remain low.  We have outline in the following graph the breakdown of callouts to a vacuum system. A system with 200 vacuum valves should have a 5{f2ac4d1e1d40dc2e2d9280a1dfa90d854b2d8c80eba743affa37fc4ce2e16def} call-out rate, meaning that there should be 10 callouts in the year.  The biggest cost here is time spent in the field finding the fault. In many projects we have found that a refresher training program for the operators can help reduce time in the field a lot. The other biggest cost reduction comes from installing a monitoring system. Have the operator being directed directly to a problem or being told ahead of time when a controller is going to fail can save significant money and resources.

    Follow Up

    If you would like to follow up on any of these points please contact your closest Flovac office.  You can contact our Operations group about audits or training courses, or just some advice about your system. If you would like to see some more information about monitoring systems you can Click Here

My Vacuum Pumps are Due for an Upgrade – What Next ?

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When a vacuum sewer system was planned in your area, there was probably an options study done showing whole of life costs. There was an expectation that over the life of the system (100 years) there would be items that would wear out and need replacing. Just as there would be components that would needs parts replaced through normal maintenance. (Asset Life)

For the rotary vane vacuum pumps, that would mean oil and filter changes. According to the pump manuals you would expect to do a fairly extensive motor overhaul at year 5 with a possible replacement at year 15. Through good care, we have seen many vacuum pumps have their lives extended considerably. That has been especially true of liquid ring pumps.

Many of the systems built prior to 1996 used liquid ring pumps (the days when water wasn’t considered a scarce resource). Since then, there has been a mixture of mainly rotary vane pumps for larger systems with smaller systems using dry running claw pumps. There have been a few outlier pumps like oil sealed screw pumps and even some rotary lobe pumps.

The vacuum pumps in your system would have been sized based on an air to liquid calculation based on the length of vacuum mains and the volume of the mains. Operationally we always look to the amount of air it takes to move the liquid through the system. A well run fully developed system should run at about an 8 to 1, or 10 to 1 air to liquid ratio. We know that if that creeps up to 30 to 1 that there is too much air in the system, and it should be tuned. A high rate like that would suggest that the vacuum pumps would be running far more than they need to. If the ratio though was lower at about 4 to 1 or 6 to 1, we would know there was too much water relative to air. This might mean the discharge pumps are running longer than they should, relative to the vacuum pumps. This might be due to I&I (infiltration and inflow) or higher flows than expected in the catchment. (Ask us for the calculation sheet for the air to liquid ratio)

With a good air to liquid ratio, we would expect the vacuum pumps to run at about 6 to 8 hours per day, in total, in a fully developed system. If your pumps are running longer than that you should check your air to liquid ratio to see what is impacting your system.

Two of the biggest mistakes that we commonly see when utilities are looking to upgrade their pumps is

  • Increasing the size of the pumps as the current run time is excessively long
  • Changing from a oil lubricated pump (R5) to a dry pump (Mink) to reduce operational costs.

Increasing the size of your pumps

This might be a great idea if done for the right reason. Talk to your engineers. If you can increase capacity at the station maybe that will allow you to accept more flows from subdivisions, new areas, higher density (more revenue).

If though you are only increasing the size because your pumps are running a long time then you need to fix the problem first. Why are the pumps running so long? Is the system tuned correctly? Are there leaks in the valves or pipework? Oversized pumps can increase the problems in a network by creating more leaks.

Once the system is tight and you have an accurate idea of your air to liquid ratio then you can make a more informed decision.

Changing to Mink Pumps

If the change is because you are using too much oil and too many filters, then it would suggest that your pump run hours are too long and you should take the steps mentioned above.

In small systems Mink pumps and their equivalent have improved substantially but in large systems where you are changing over from R5 630 pumps or their equivalent there are a number of downsides that utilities are now discovering.

In the larger sizes the Mink pumps run a lot hotter and potentially noisier. The heat has an impact on pipe materials in the station, venting of the station, and will badly affect odour control measures.

On larger systems there is a limit to the depth of vacuum that these type of pumps will achieve and often the result is an increase in energy use and pump run hours.

Some utilities have also tried the addition of variable speed drives in their pumps as a way of increasing vacuum in the lines and decreasing line flooding. The speed is often varied due to the amount of vacuum pressure in the lines or at the end. It is rare to see this used in wet/sewer type systems and is more common in dry/food processing applications. As vacuum sewers are based on a ratio of air to liquid, the use of a VSD disguises problems in the system and can ultimately increase problems in the networks.

Upgrading of your vacuum pumps is inevitable – we can help you with finding the right solution for your system

Call our Engineering or Operations Group to organise the following as a first step.

  • System Audit To correctly size the vacuum pumps an analysis of the air to liquid ratio is needed. The system needs to be air tight to do this. If there are leaking vacuum valves, due to old age, air leaks in the pump station or elsewhere, these need to be fixed prior to any upgrade as any larger or new vacuum pumps could make these harder to find and just lead to higher energy costs and high oil use. An Audit will check the current state of your system; give you an understanding of what will be required to accomplish the outcomes you want
  • Capacity Audit What was the system designed to handle, what can it potentially handle for the next 15 years.

To read more about Upgrades Click Here

1,000,000 cycles. How long should your vacuum valve last.

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A vacuum interface valve is located in a collection pit usually outside of the property boundary at the side of the road. In most systems this collection pit is connected to 4 to 6 homes via a gravity pipe connection.

Although the vacuum system is designed so that the vacuum valve allows for a flow of .25 litres per second (4 gallons per minute) from the houses. There are some occasions where parts of a system may be designed for higher flows. This may come from schools, commercial areas, gravity fed or pumped flows. Our engineers are very careful about how these higher flows enter the system.

The vacuum valve is designed to activate pneumatically once 40 litres (10 gallons) enters the collection pit. This allows for a mix of air and water to enter the system with the correct air to liquid ratio so that the vacuum mains do not flood with too much liquid. In an average residential community, the vacuum valve will activate between 80 and 100 times per day. This is based on the average flow per house and the number of houses per collection pit.

Flovac Manager Georg Sarap checking the monitoring system via the touch screen at the vacuum pump station

For maintenance we recommend that certain parts in the valve and controller are replaced every 10 years or 300,000 cycles. The body itself has a design life of 50 years. European Standard EN 16932 calls for an endurance test with 250,000 cycles, as does the Australian Standard AS 4310 Details Here

Flovac has independant testing of the valve at 700,000 cycles, significantly more than required by the standards and represents 23 years of activation without failure.

We know that in a number of our systems we have some very high flow situations. With some its been due initially to infiltration which clients have since resolved. With others the system has been designed to cater for very high flows. High Flow Projects .

One Million Cycles

Monitoring screen showing over 1 million cycles

At our project at Leppneeme in Estonia our team has been watching one of our high flow valves closely. It has a Flovac cable monitoring system which can tell the operator the number of times the valve has operated (Tsuklite arv:). It can also alert the operator to any faults, tell the temperature in the pit, the power use and location. The pit is located very close to the vacuum station which makes it easier to handle very high flows. This week the valve passed its 1 million mark with number of cycles. Based on these activations it has done 34 years worth of work in just 8 years and is still going strong.

Fortunately the operator would be able to tell from the monitoring system if any parts were wearing as the open time of the valve would start to change.

Although we have other systems that have valves which have recorded over 1 million cycles as well as achieving this result on our test bench it has been great watching it tick over via our monitoring system.

Flovac Vacuum Valve and Controller

Rehabilitating Old 2-inch Vacuum Systems

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Those engineers thinking that vacuum sewer technology is new, may be surprised to learn that there are still a number of operating systems installed in the late 1960’s and 1970’s.

These early systems were installed using 2-inch vacuum valves rather than the 3-inch (80mm) vacuum valves commonly used today. The modern inventor of vacuum systems Joel Liljendahl wanted to separate grey (shower/laundry) water and black(toilet) water using vacuum. A 2-inch valve was sufficient for this use and Electrolux who bought the patent started using the 2-inch valve in a number of projects through The Netherlands, Germany, the Caribbean, Australia and the USA.

As a testament to the technology, many of these original projects are still operating, though not as well as modern systems. The same would be said for any technology (cars, computers, televisions).

Sylvania Waters Australia

In 1968 one of the worlds largest 2-inch vacuum systems was installed at Sylvania Waters, 12 km south of Sydney Australia. The vacuum valves in fibreglass pits collected wastewater from 2 houses sending it to the vacuum pump station. The early system used a ball float controller, similar to what was used in old toilet cisterns. As this was not a separated grey/black water system, a 2-inch valve was clearly going to be a choke point with a 3-inch toilet drain pipe. In 1994 we were hired by Sydney Water to fix up the system, replace the valves and float controllers. Sadly because of the collection pit size and the vacuum main size it was not possible to increase the valves to 3 inch, but the system was improved.

Now, with it being over 50 years old, some really positive changes can be made, specifically with the help of monitoring systems.

Even though most vacuum regulations call for a minimum sized valve of 3-inches there have still been some 2-inch and 2 1/2-inch valve systems installed. You have all met that client who wants to save $100 on a valve but doesn’t care that the utility will have to spend a fortune on maintenance trying to clear blockages. This has not helped the reputation of vacuum systems and we often hear of problem systems and high maintenance costs. Quite often it is due to small or bad quality valves or old fashioned ball controllers still being used.

Reusel, The Netherlands

One recent system replacement we made was in the village of Reusel in The Netherlands. The system was not that old, but the 2-inch valves had a lot of blockages, ball float controllers were used and there was no integrated monitoring system. Our team in the Netherlands has managed to upgrade the system and reduce operational costs considerably.

If you have an old 2-inch system. Contact us at [email protected] and we can give you more details about what can be done to help.

Pump Station Information captured for the operators and managers

Vacuum Sewer Operations Manager Interview

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Alistair Read, Wastewater Utility Manager swapping old for new

Alistair Read, Wastewater Utility Manager swapping old for new

Interview with Alistair Read – Operations Manager Coorong Quays, South Australia.

Coorong Quays Project Link

1. What is your role at Coorong Quays?

I am the Manager of Operations of the Coorong Quays canal development in charge of the vacuum sewer system as well as the Treatment Plant. With the vacuum sewer system I am involved with the installation through to the tuning of each stage. I also review the specific design by Flovac and local engineer Wallbridge Gilbert Aztec (WGA). At this stage it is a private development and we have operated as a private utility.

2. How long has your vacuum sewerage system been in operation?

This vacuum system has been in operation since 1990 at Coorong Quays. It was originally known as Marina Hindmarsh and attracted a lot of holiday makers from Adelaide. It was the first vacuum system installed in South Australia. I have had 22 years of personal experience in operating this system. Starting out with Stage 2 with 36 Pits to Stage 8 with 276 Pits now servicing 845 homes. I have supervised seven stages, including the building of two of the three vacuum pumping stations. We also use the vacuum system to suck the wastewater off boats at the marina as well as many of the houseboats which travel up the Murray River.

Kangaroo Island bushfires

3. What do you do when not managing the system at Coorong Quays.

I am very active with the Army Reserve and often need to be away with the Reserve. Earlier this year I was tasked to bushfire assistance at Kangaroo Island. It was a devastating period. I also love camping in the northern part of the state. It is incredibly beautiful. When I am away for extended periods I know I can rely on Flovac helping out my team, and I can also keep in touch via the monitoring system if I have coverage.

4. What are some of the main benefits of the Flovac Vacuum Sewerage System in your view?

There are many benefits of the vacuum system. It has a number of environmental benefits: It’s ideal for high water tables with typical trenching of 0.9 to 1.2 to 1.5 range, for the main lines. It’s specifically suited to coastal tidal areas and environmentally sensitive areas. For example, if there is any third-party major breach, that line flow will stop due to a lack of vacuum. This means the spillage impact is minimal in the area as it is a gravity system with vacuum assisting. Far less than conventional Gravity/Pressure or LP system, where the environmental impact could be greater, so the Flovac Vacuum System is ideal for such locations.

It is also ideal as it has minimal environmental impact for sensitive areas like Coorong Quays where the development borders on the Coorong and the Murray River. It is also a very cost-effective system to operate. It takes a smaller team to run, without needing heavy specialized equipment. Thus, keeping maintenance asset costs down.

We operate everything at the development under ISO 14001, which is an environmental certification. This governs many aspects including health and safety. The vacuum system helped with the certification. That it cant leak, no infiltration, low power use and very good from a health and safety perspective was all very important.

5. Why did you choose this system over other possible options?

Manager Alistair Read at an old styled concrete chamber with Flovac valve

In comparison with Gravity and LP sewer systems we are very happy with this system, as it has the flexibility for ‘add-ons’ to initial plans. You can tune this system to work for your purposes. For example, until recently Coorong Quays had a low population in winter, with higher numbers in summer.

The system needed to be tuned to fit in with this and thus reducing operating cost it has been more energy efficient. This vacuum system has the ability to have an auto air injected system to assist with this over the ‘High season’. This system is highly flexible.

We have recently experienced some social changes from having a ‘transitional’ population to more permanent residents. This has occurred because of lifestyle changes and with the current COVID-19 situation people are now working from home at Coorong Quays coupled with increased domestic holidaying.

This system has worked well for us as it has allowed us to cope with this social change, and with changing housing designs now being built, that includes more bathrooms, bedrooms etc.

6. What do you think of FVS systems in general?

This system is a robust one that also has the ability to be flexible’ in coastal terrains. It can be designed to better fit in with the land contours.

For example, in the case of Coastal it can be designed with minimum disturbance, as opposed to conventional system installations. From an operations viewpoint it is also easy to maintain with a smaller crew.

Maintenance is recommended annually. With rebuilds 10 -15 years for internal components, depending on cycle usage.

From my experience with valves, it’s about 15 years with nominal use of 30,000 to 40,000 cycles per valve a year.

7. Would you recommend this particular system to other similar developments such as yours?

Flovac Monitoring System

I highly recommend this system for coastal environments. Used in conjunction with the wireless monitoring system (FMS) it is an even better way of monitoring this system and tuning it to run at its optimum. The benefit of this is that it can be done remotely, and tuned on site.

The FMS electronic monitoring system also records how the valve activity is performing and allows the operator to address any maintenance issues straight away.

8. Has Flovac provided good support to you and your team?

Flovac have been with us all the way through. New product developments like the monitoring system and PE collection pits. Improvements to their valve and controller and  their engineers and operators have been fantastic. They run 24-hour support, though we have never really needed it.

It’s important to recognise that a vacuum system is not just a single product, its a system. So we need to be on top of all aspects. I have plenty of other things to watch over in my life so its been great knowing that we can rely on the Flovac team. They are doing this day in, day out , all around the world. They know what they are doing and they have never let us down.

Coorong Quays residential canal development project in South Australia

Is Infiltration Causing Problems in Your Sewerage System?

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Not long after Miles Crossing Sanitary Sewer District in Oregon installed a new vacuum sewer system they realized they had an issue that needed an immediate fix. According to the superintendent, Carl Gifford, “Our flows exceed 180,000 gallons [on heavy rain days] due to a massive I/I issue that we grew to have”.  This excess can put a strain on the system which can increase utility bills, not to mention, Miles Crossing is a collection system only.  They have to work with a neighboring system for treatment and have a limit on max flow that can be sent.

Flovac and Miles Crossing were able to meet and come up with a  plan to utilize Flovac Monitoring System to overcome these issues.

“With this system, we can monitor the fires from each individual pit. During a rain event, it is really simple to tell which ones contribute to the massive I/I we are dealing with. During the last winter, we were able to identify 9 sources of I/I that we were able to repair”.

Gifford also mentions how the system allows for the sewer district to know about problems before customers do. “An additional benefit that we observed with this system is the alarms that it provided. Numerous times we were called out for a high-level at a residence and were able to make the repair and get it back online before the customer knew there was a problem. This helps greatly with the risk management of possible failures and the following lawsuits that have happened in the past”.

Due to less load on the system, Miles Crossing have been able to add residential connections creating revenue.

To find out more about the Flovac Monitoring System – Click Here

Image on Front Cover Torsten Blackwood—AFP/Getty Images