Hand pump for filling solar systems – how to properly fill and bleed the circuit
Manual pump for filling solar systems – complete guide on how to properly fill and purge the circuit
Filling the solar circuit with antifreeze fluid may seem like a simple step at first glance – but it is precisely here that errors occur, which then cause problems for years. Air bubbles in the collector, insufficient pressure, poorly mixed fluid, incorrect purging – these are all things we regularly see in practice. Most of them could be avoided if the filling procedure was correct from the beginning.
This article focuses on the manual pump for filling solar systems – what it is, how it works, why it is better than improvised solutions, and most importantly: what is the correct step-by-step procedure for filling and purging the primary solar circuit. If you have never done it before, or if you feel that your system is not filled correctly, read on.
Why proper filling of the solar circuit is so important
The primary solar circuit – that is, the piping between the collector and the storage tank (or heat exchanger) – is a closed system filled with antifreeze fluid based on propylene glycol or ethylene glycol. Unlike a heating system with water, we are working with a fluid that is more expensive, has specific properties, and must be in the circuit without air bubbles.
Air in the solar circuit is a real problem. Air pockets settle in the highest points of the route – typically directly in the collectors. A collector without fluid can heat up to 180–200 °C or more on a sunny day, leading to stagnation. During stagnation, the fluid in the collector evaporates, the steam pushes into the pipes, and when the collector cools down, it can lead to reverse air suction or degradation of the fluid due to extreme temperatures. Repeated stagnation shortens the life of the fluid and seals.
Along with air bubbles, the correct operating pressure is also important. Most solar systems require a pressure of 1.5–3 bar depending on the installation height and the type of expansion vessel used. Too low pressure means the pump is "pushing air," not fluid – the system circulates inefficiently. Too high pressure strains the safety valve and seals.
And finally – the concentration of the antifreeze mixture. The fluid must be mixed in the correct ratio (typically 40–50% glycol) to withstand frost, while at the same time maintaining good heat transfer properties. You will learn more about this in the article Filling a solar system with antifreeze – what you need to know.
How a manual pump for filling solar systems works
A manual pump for filling solar systems is a simple but well-designed tool. It is not a garden pump or a tire pump – it is a device specifically designed for working with glycol-based fluids under pressure.
The principle is as follows: the pump has a tank (reservoir) for the fluid – usually with a capacity of 10–20 liters – and a piston or membrane mechanism that manually (lever or rotary drive) pumps the fluid from the tank into the system through a hose with a quick coupling. A pressure gauge is mounted on the hose (or on the body of the pump), so you can monitor the pressure the pump creates.
Key feature: the pump is able to create and maintain pressure in the range of 0–6 bar (depending on the model), which is more than sufficient for solar systems. Unlike filling by gravity (from an open container), here you have full control over the pressure and can regulate it.
An important part of the pump are check valves, which prevent the reverse flow of fluid from the system back into the reservoir. Without them, with each piston stroke, the fluid would flow back, not into the circuit.
A hose with a quick coupling or threaded end is located at the pump outlet, which is connected to the system's filling valve. On the other side of the system (or another valve), air or excess fluid is drained. In this way, you push the fluid in one direction and expel the air in the opposite direction.
If you are looking for a specific product, see Manual pump for filling solar systems available in the expansion vessels and pumps category – a robust solution for professional and home installation.
What you will need before filling – list of tools and materials
Before the actual filling, prepare everything you need. Nothing is more annoying than stopping in the middle of filling because you are missing a wrench or a bucket to catch the fluid.
- Manual pump for filling solar systems – main tool
- Antifreeze fluid in the correct concentration (ready-made mixture or concentrate to be diluted with distilled water) – the amount depends on the system volume; a typical two-collector system has a circuit volume of 8–15 liters
- Measuring device for glycol concentration – refractometer or hydrometer; you check the actual concentration of the mixture before filling
- Thermometer – to check the fluid temperature (we fill it cold, below 30 °C)
- Hoses and reducers – to connect the pump to the system's filling valve
- Wrenches and screwdrivers – to open purge valves, adjust flow on balancing valves
- Bucket or container to catch air and fluid – when purging, fluid comes out with air
- Clean rags or paper towels – glycol fluids are difficult to clean once they dry
- Notebook or mobile phone for taking photos – note down the pressure after filling, concentration, date; you will need it for service inspection
If you are talking about the volume of the liquid, you need to know the volume of the primary circuit. How do you find it out? The volume of the storage tank and collector can be found in the technical documentation. The volume of the pipes can be calculated easily: for Cu18 (18 mm copper pipe) it is about 0.2 liters per meter of length, for Cu22 it is about 0.3 l/m. Add them up and then add the volume of the heat exchanger and collector (typically 1–3 liters). A more detailed calculation procedure can be found in the article What expansion tank volume do I need for my solar circuit.
Schematic connection of the pump to the solar circuit
In the diagram you can see the basic connection: the pump is connected via a hose to the filling valve (so-called filling and draining valves), which is located on the pumping station – usually on the inlet (cold) return pipe. Air venting takes place at the highest point of the circuit, i.e., at the collector or just below it.
Step-by-step procedure for filling the solar circuit
1. System preparation before filling
Before filling, check whether all connections and valves are tightened and the seals are in place. Nothing is worse than filling a system with a leak – the fluid leaks out, you keep pumping over and over, and the pressure does not drop. Also check that the solar pump in the pumping station is switched off (it must not run during filling – it starts working only after the system is filled).
Check the pre-charge pressure of the expansion tank. Before filling the system, the expansion tank must have the correct pre-charge pressure – typically 0.5–1 bar higher than the static pressure of the fluid column from the expansion tank to the highest point (collector). How to set it correctly is described in the article Setting the pre-charge pressure in the solar system expansion tank. If you do not set the pre-charge pressure before filling, the expansion tank membrane may not work correctly and the system will not have a reserve for the thermal expansion of the fluid.
All closing valves on the primary circuit must be open. Leave the air vent valves (automatic or manual) open – the air must have somewhere to go. If you have automatic air vents at the collector, check that they are functional and open.
2. Pump and fluid preparation
Fill the pump reservoir with the prepared antifreeze. Before filling into the reservoir, check the concentration with a refractometer – for our conditions we recommend protection down to –28 to –35 °C, which corresponds to approximately 40–50 % propylene glycol. The fluid must be clean, free of impurities and old glycol (do not mix old and new glycol solutions without prior testing).
Connect the pump’s output hose to the system’s filling valve. Open the filling valve. On the opposite side of the circuit (or at the air venting point) prepare a bucket to catch the fluid that will flow out – it will flow out together with air.
3. First flushing filling (air removal)
Start pumping slowly and evenly. The goal of the first phase is not to reach the operating pressure, but to push out as much air as possible from the circuit. The fluid enters from below (from the pumping station) and pushes the air upwards towards the collector.
During the first filling, leave the air vent valve at the collector open (or manually vent the collector). At first, only air will come out of the vent, then air with fluid, and finally only fluid. At that moment, close the valve.
Repeat this “flushing” filling for each branch of the circuit if you have multiple collectors or multiple rows. Open one row, fill it, close it. Then the next one. Never fill all branches at once, because air will always find the path of least resistance and some areas will remain unvented.
4. Pressurization to operating pressure
When the system is pre-filled and air is expelled, proceed to set the operating pressure. Continue pumping until the pressure gauge on the pump (or the manometer on the safety group) indicates the desired value.
What is the correct operating pressure? It depends on the installation height and the pre-charge pressure of the expansion vessel. In general:
- Collectors up to 5 m above the safety group → operating pressure 1.5–2 bar
- Collectors at a height of 5–10 m → operating pressure 2–2.5 bar
- Collectors above 10 m → operating pressure 2.5–3 bar
The operating pressure must be at least 0.3–0.5 bar higher than the pre-charge pressure of the expansion vessel. For example: expansion vessel pre-charge pressure 1.5 bar → minimum cold system filling pressure 1.8–2 bar. The system safety valve (typically 6 bar) must be clearly above this pressure.
A detailed calculation can be found in the article How to choose an expansion vessel for a solar system – key criteria, where the relationship between pre-charge pressure, filling pressure and the volume of the expansion vessel is also discussed.
5. Air venting with the pump running
This is a step that many amateur installers skip – and it is precisely here that most problems arise. After filling and reaching the operating pressure, start the solar pump. The pump will begin to circulate the fluid and mechanically move air bubbles that remain trapped in dead spots of the circuit (bends, rising pipes, collectors).
Let the pump run for 10–15 minutes, then vent again – at each automatic air vent and at manual ones. The pressure in the system will drop during venting (air escapes, fluid volume decreases) – you will need to pressurize again using the pump. This cycle may need to be repeated 2–4 times until the system is truly free of air.
An experienced installer knows that a collector never releases all the air during a single filling. Air hides between the absorber fins and is gradually released during flow. Therefore, the first few hours of operation, the system will slightly "gurgle" and the automatic air vents will work actively.
6. Final inspection and recording of parameters
After completing the air venting, check the following:
- System pressure in the cold state (no sun, pump off) – record it
- Fluid temperature when measuring pressure (pressure changes with temperature)
- Glycol concentration measured with a refractometer (take a sample from the air vent valve)
- Visual inspection of all connections for leaks
Record these data in the operating log or attach a label directly to the pump station. In a year or two, when the service inspection comes, you will know what the condition was at the time of filling and whether the pressure has changed.
Typical mistakes during filling – what happens in practice
Over the years of practice, we have seen all sorts of situations. Here are the most common mistakes people make when filling solar systems:
Filling without opening the air vents. Air has nowhere to go and is only compressed into a "pocket" at the highest point. The system is filled, the pressure reaches the desired value – but the collector is still full of air. In the sun, the collector heats up, the air bubble is pushed down, the pump stops flowing (air blocks the flow) and the controller reports an error. The customer calls service, thinking the pump is faulty.
Mixing old and new glycol. An old glycol solution (after several years of operation) is acidic and degraded. When you mix it with fresh fluid, you slow down the degradation, but you don't stop it. The correct procedure is: drain the old fluid, flush the circuit with clean distilled water, then fill it with a fresh mixture.
Incorrect concentration of the mixture. We have seen systems filled with 100% glycol (without dilution), because the installer "rather gave more, so it would withstand the cold". A 100% glycol solution has much worse heat transfer properties and higher viscosity – the pump has problems with flow and the heat exchanger works inefficiently.
Filling when hot. Never fill a solar circuit if the collectors are hot (for example, in summer at noon). A glycol solution entering a hot pipe system can immediately start boiling and creating steam, which completely invalidates the filling. Fill in the morning, in the evening or in cloudy weather.
Incorrect pre-charge pressure of the expansion vessel. If the expansion vessel does not have the correct pre-charge pressure before filling, the membrane may not work properly after the system is filled. Result: when the fluid heats up, the pressure rises sharply (the expansion vessel does not perform its function) and the safety valve opens. More about this problem in the article Common expansion vessel and solar pump failures – causes and solutions.
Advantages of a manual pump compared to other filling methods
Gravity filling, in which liquid is poured into the system from a container placed higher up and air escapes through an open valve, seems simple at first glance – but in practice, it works only for the simplest pipe layouts. For any larger installation where the collector is located more than 3 m above the tank, gravity filling is unreliable and often incomplete. Air remains trapped and the system operates inefficiently.
An electric pressure pump is an alternative to a hand pump – faster, but more expensive and requiring power supply. For a typical home plumber or a small company, a hand pump for filling solar systems is the ideal compromise between cost, simplicity, and efficiency.
Maintenance and refilling – when to repeat the process
Solar antifreeze is not eternal. Propylene glycol degrades over time – it oxidizes, its pH drops, and corrosion inhibitors are depleted. The recommended fluid replacement interval is 5–8 years, but it depends on how often the system stagnates (stagnation accelerates fluid degradation).
How can you tell that the fluid needs to be replaced? Take a sample (from the air vent) into a glass container and look at it: fresh fluid is clear, yellowish to greenish. Degraded fluid is dark, brown, may have sediment or a burnt smell. For accurate pH measurement, use test strips – the correct pH value is 7–9. Below pH 7, the fluid corrodes metal parts of the system.
The refilling procedure when replacing the fluid is almost the same as the first filling, with one added step – draining the old fluid. Drain it through the drain valve into a suitable container (glycol solution must be disposed of in an environmentally friendly way, not poured into waste), then flush the system with distilled water and refill it with fresh mixture.
Even during routine annual checks, it is good to check the pressure. If the cold system pressure has dropped by more than 0.3 bar since the last reading, the system is losing fluid somewhere or has an expansion vessel problem. Routine pressure and expansion vessel checks are described in the article How to check and maintain the expansion vessel in a solar system.
Safety rules when working with antifreeze
Propylene glycol is a relatively safe substance (considered food-safe), but ethylene glycol is toxic and dangerous upon contact with skin or mouth. Always read the safety data sheet (SDS) of the fluid you are using before working with it.
Wear rubber gloves and goggles when handling the concentrate. When spraying fluid under pressure (when opening the air vent), keep your face away from splashes. Catch the fluid in a bucket, do not let it drip on the floor – it is slippery.
When working on a roof (where collectors are usually located), follow safety rules for working at heights. The filling pump and fluid are usually located at the station – but venting at the collector requires access to the roof, always with proper safety equipment.
Never open any valve, safety or air vent, when the system is hot and under pressure. Boiling fluid may spray out. Perform all work on a cold system.
Most frequently asked questions (FAQ)
What hand pump do I need for a typical two-collector home system?
For a two-collector system with a circuit volume of about 10–15 liters, a standard hand pump with a 15–20 liter tank and a pressure output of up to 6 bar is sufficient. The hand pump for filling solar systems available at atria.sk is specifically designed for these applications – it handles typical home and larger installations without problems.
Can I fill the solar circuit with regular water instead of glycol mixture?
Technically yes, but in practice it is a mistake. Water will freeze and pipes will crack in the cold. Moreover, regular water does not contain corrosion inhibitors that protect copper, aluminum, and steel in the circuit. Distilled water without additives is slightly better, but still offers no protection against freezing. The only correct filling for a solar primary circuit is a certified glycol solution in the correct concentration.
What pressure should I set when filling and how does it affect the expansion vessel?
The cold system operating pressure must be at least 0.3–0.5 bar higher than the expansion vessel pre-charge pressure, and at the same time must ensure sufficient pressure at the highest point of the system (the collector), to prevent cavitation. For a typical installation with a collector up to 6 m in height and an expansion vessel pre-charge pressure of 1.5 bar, set the filling pressure to 2–2.5 bar. Detailed calculations can be found in the article Mounting an expansion vessel in a solar system – step by step.
What should I do if the pressure in the system drops quickly after filling?
A rapid pressure drop after filling indicates a leak – check all connections, valves, collectors (solar collectors may have microcracks from winter damage), and the safety valve (sometimes leaks during pressure shock during filling). If the pressure drops slowly (over weeks), the problem may be in the expansion vessel – a burst membrane or lost pre-charge. More about this can be read in the article Common expansion vessel and solar pump faults – causes and solutions.
How much fluid will I need to fill a typical home solar system?
For a typical system with 2 flat collectors (each about 2 m²), 8–12 meters of Cu18 piping, and a 200–300 l tank with one coiled pipe, expect a primary circuit volume of 10–15 liters. Always prepare 20–30 % more than the calculated volume – fluid is lost during venting and needs to be topped up.
Is it necessary to vent the solar circuit during operation, not only during filling?
Yes, especially in the first few weeks after commissioning. Air gradually escapes from the fluid, and automatic vents can remove it on their own. If you do not have automatic vents (or they are clogged), manually vent the system after the first and second month of operation. Later, once a year during routine service is sufficient. A detailed annual inspection is described in the article How to check and maintain the expansion vessel in a solar system.
Conclusion – proper filling as the foundation for long system life
A hand pump for filling solar systems is a simple but indispensable tool. It is not an unnecessary expense – it is a guarantee that the solar circuit will work as it should from the very first day. Without air bubbles, with the correct pressure, and with fluid in the correct concentration.
A solar system that is properly filled, vented, and regularly checked from the beginning can operate reliably for 20 years or more without major problems. A system that was filled quickly, not properly vented, and then forgotten will show up in a year or two – either with a pump failure, degraded fluid, or a cracked collector after winter stagnation. An investment in the right tools and the right procedure therefore pays off many times over.
If you are planning your first installation or servicing an existing system, all the necessary tools including