Why the suction pipe connection is more critical than the discharge
When I deal with domestic water supply installations with customers, I almost always encounter the same situation: the pump is new, the motor is running, but the suction performance is poor or the pump won't even start. Usually after ten minutes of inspection, I find the cause on the suction side – a loose hose, missing gasket, wrong diameter, too long suction, or an unsuitable coupling. The discharge side can cope with many deficiencies because the pump works under pressure there. The suction side is a completely different story.
Suction works on the principle of vacuum – the pump "creates a vacuum" and the atmospheric pressure on the water surface in the well or tank pushes the water up into the pump. Since atmospheric pressure is fixed (approx. 1 bar = 10 m water column), every leak, every air bubble, or too narrow hose cross-section immediately degrades the suction performance. A leak on the discharge side causes water leakage. A leak on the suction side causes loss of suction – and that is a much more dangerous problem, because no water leaks out, the problem is only functional.
In this article, we will go through the entire process of properly connecting the suction pipe step by step, from selecting the hose through the correct couplings to testing tightness. We will also address the most common mistakes from practice and how to quickly detect and eliminate them.
Basics of the suction principle – what you need to know before you reach for the tools
Suction of the pump is physically limited. The theoretical maximum suction is 10.33 meters (at 15 °C), in practice you will get at most 7–8 meters of clean suction height, because you have to subtract pressure losses in the hose system, resistance of the check valve, narrowing of fittings and water height. Warm water (above 30 °C) further reduces the suction range, because the saturation pressure decreases.
This leads to practical tip No. 1: place the pump as close as possible to the water level. Every unnecessary extra meter of suction height reduces the flow and increases the risk of cavitation. If you have a well with a depth of 6 meters and the pump is standing two meters above ground, the real suction height is 8 meters – and that is on the edge of what a standard surface pump can handle.
Practical example: a customer in the Nitra region had a 1,000-liter plastic rainwater tank buried in the garden, with a water level of about 1.2 meters below ground level. The pump was right next to the tank on the ground surface, so the suction height was only 1.2 m. Despite this, the pump did not start. Cause: an 8-meter suction hose ¾" was twisted and in one place bent into a sharp corner, which caused an air bubble that the pump could not compress at start-up. One straightening and shortening of the suction line to 4 meters solved the problem.
Selection of suction pipe – diameter, material and length
The first and most important choice is the diameter of the suction pipe. Many installers want to save money and reach for a narrower hose "because garden hose 1/2" works as well on the discharge." This is a classic mistake. The suction hose must have the same or larger diameter as the pump inlet – never smaller.
- Pump inlet 1" (25 mm): minimum suction hose 1" – ideally 1¼"
- Pump inlet 1¼" (32 mm): minimum suction hose 1¼" – ideally 1½"
- Pump inlet 1½" (40 mm): minimum suction hose 1½" – ideally 2"
- For simple garden pumps with ¾" inlet: suction hose ¾"
Watch the length: every meter of suction hose means pressure loss. Approximate rule for PVC braided suction: at a diameter of 1" and a flow of 50 l/min, the pressure losses are approx. 0.1 bar per 5 meters. With a long suction of 15 meters, you will lose 0.3 bar just from friction – and this is critical at suction heights of 6–7 meters. The suction hose should ideally not exceed 8 meters; if the situation requires a longer one, increase the diameter by one size.
The material of the suction pipe must be rigid in the cross-section – it must not collapse under vacuum. Garden hoses are not suitable! For suction, use:
- Spirally reinforced PVC hose (suction hose): has a ribbed reinforcement of spiral PVC or steel wire – designed directly for vacuum, cost-effective
- Stiff plastic pipe (PP, PE, PVC): excellent stiffness, minimal losses, best choice for long suction
- Thick-walled EPDM hose: frost resistance, suitable for lower temperatures
Never use a regular garden hose without spiral reinforcement for suction – under negative pressure it will compress and lose cross-section. On the countryside, I see these improvisations quite regularly, always with the same result: the pump runs dry.
Couplings and fittings on the suction side – where every leak counts
On the discharge side of a garden installation, GEKA 3/4" brass bayonet hose couplings are particularly popular due to their speed and reliability. On the suction side, their use requires greater care, because here we must achieve absolute tightness – every microleak of air is enough to lose suction.
Basic rule: the fewer joints on the suction hose, the better. Each joint is a potential entry for air. An ideal suction hose has one joint at the pump and one at the bottom of the well, plus a check valve – nothing more.
For threaded connections on the suction side, never rely on the thread seal alone. Use either high-quality PTFE (teflon) tape in 4–5 layers or traditional hemp fiber with anaerobic sealant (Loctite 577 or equivalent). Anaerobic sealants are especially suitable for suction, because their curing occurs precisely in the absence of oxygen – that is, right in the thread, where you need it.
For hose couplings with clamps – ALWAYS use stainless steel clamps (not cheap plastic clamps). Place the clamp at least 15 mm from the end of the hose, tighten evenly. Before sliding on the rubber hose, apply a bit of vaseline or soapy water, don't force it dry – you risk damaging the edge of the hose, which causes a leak.
For quick couplings of the GEKA type – for example, GEKA 1" hose bayonet brass coupling or variants with external thread like GEKA 3/4" coupling with external thread – the rule of checking the rubber applies. The bayonet seal is usually made of NBR rubber and after a few seasons it ages, hardens and cracks. Before each seasonal start, pull out the rubber, inspect it and if it is hard or cracked – replace it. A new gasket costs a few cents, a ruined season costs much more.
Check valve on the suction side – a necessity, not an accessory
A check valve at the end of the suction pipe (so-called suction basket with a valve, or a separate check valve) is absolutely necessary for the proper functioning of the pump. Its role: it prevents the water from the hose from flowing back into the well after the pump is turned off. Without it, you have to prime the entire suction at every start – which is not only annoying, but also leads to dry running and damage to the pump.
In practice, I see two situations: either the check valve is completely missing (in improvised installations), or it is present but clogged with mud and non-functional. A suction basket with a filter mesh should be cleaned at least once a year – ideally in spring before the season. A clogged mesh reduces the cross-section and directly reduces the suction performance.
Important: always place the check valve as close as possible to the lower part of the suction pipe – ideally directly at the end of the suction basket. If you put it closer to the pump (which some improvise), the entire column of water in the hose below it will drain out at every shutdown and at the next start you have to fill the entire suction column again – this is overlooked even by more experienced people.
Step by step: the process of properly connecting the suction pipe
Here is a proven procedure that I use for installations. Skipping any step is almost always a source of later problems.
1. Measure the suction height and plan the route. Determine the vertical distance from the water level to the pump inlet. Add 1 m for each 90° elbow and 0.5 m for each 45° elbow. The result must not exceed 7 m at room temperature and 6 m at warm water. Plan the route so that the suction hose rises smoothly without "humps" – an air bubble trapped at the top of the bend will cause loss of suction.
2. Choose the correct hose diameter. According to the diameter of the pump inlet and according to the rule of the same or larger. For longer suction, always one size larger.
3. Install the check valve/suction basket. At the end of the suction pipe, at least 30 cm below the minimum water level (otherwise you will suck air when the level drops). Turn the suction basket with the filter down.
4. Seal each joint. Threaded joints: PTFE tape or anaerobic sealant. Hose joints: double stainless steel clamp. Check that the threaded joints are tightened – but not over-tightened, especially with plastic pump bodies.
5. Fill the suction with water (priming). Through the priming opening or by removing the hose from the pump, pour water into the suction line until it runs out of the pump inlet. This is a critical phase – the pump must not run dry.
6. Start the pump and monitor. Listen – a uniform acceleration of the sound and stabilization after 5–15 seconds is correct. Cavitation sound (intensive crunching/crackling) indicates a problem. Turn off, look for a leak.
7. Check the pressure. A manometer on the discharge should show a stable pressure corresponding to the height geometry and flow. Fluctuating pressure or pulsation = air in the suction.
Most common mistakes in practice and how to recognize them
Over the years of practice, I have encountered recurring mistakes. Here are the ones I see most often:
Garden hose instead of suction pipe: A garden hose (even thick-walled) is not dimensioned for vacuum. Collapse can only be prevented by spiral reinforcement. Symptom: the pump sucks for a while, then the flow drops to zero – the compressed hose has stopped the flow.
Too many elbows on the suction: Each 90° elbow is equivalent to 1.5–2 meters of straight hose in terms of pressure losses. I have seen installations with four elbows, where the effective suction length was 12 meters instead of real 4 meters. Result: the pump did not suck even from a 3-meter depth.
Missing gasket on the threaded connection: A classic. The thread looks tightened, but air slowly enters through the thread grooves. Symptom: the pump starts, but after a minute the flow drops – air is gradually getting into the suction.
Check valve too high: A check valve placed near the pump, not at the end of the suction basket. When turned off, the entire suction below the valve drains out. Symptom: after each shutdown, you have to prime. The customer thinks the pump is "broken".
Wrong direction of the spiral hose: The suction hose has a spiral designed for strength in one direction of twisting. If it is twisted the opposite way, the reinforcement can loosen. Solution: during installation, watch that the hose lies naturally without forced bending.
Clogged suction basket: A customer in the Trnava region had a well with mud, where the suction basket had not been checked for 4 years. The mesh was practically completely clogged with bacterial film and sediment. The pump was running, but the suction performance was 30% of the nominal value.
Tightness of the suction system – how to properly check without special tools
The professional method is a pressure test using a vacuum gauge – a measuring device for negative pressure connected to the pump's suction inlet. If the suction system holds the vacuum, the valve is tight and the suction will work. Without a vacuum gauge, you can do a simple test:
Soap water test (air side): Before priming, when the suction is empty, block the pump outlet and pull out the suction basket from the water. Blow into the suction (e.g. through the hose connection on the pump using a low-pressure compressor 0.3–0.5 bar). Rub all the joints with soapy water and watch where bubbles form. Every bubble = leak. This is the same method as for testing gas pipes.
Visual inspection during operation: When the pump is running, watch the water jet – if it is full and even, the suction is tight. If there are air bubbles or pulsations in the jet, air is getting into the suction. With a transparent suction hose (some PVC hoses are transparent), you can directly see the air bubbles and locate their source.
Manometer method: Install a manometer on the discharge. Stable pressure = tight suction. Pulsing or decreasing pressure under constant conditions = air in the suction.
Special situations: tanks, catch basins, open sources
The water source is not always a deep well. In garden installations, I come across several scenarios:
Plastic underground rainwater tank: The water level fluctuates according to the weather – today 0.8 m, in a month after drought 1.8 m. The suction basket must be long enough to reach below the minimum expected water level. Do not forget to leave a reserve – when the water level drops below the suction basket, the pump will start sucking air. Solution: a level switch that turns off the pump when the water level drops below the minimum.
Open garden tank or pond: Here the check valve is especially important, because in a normal garden, dirt, leaves, insects or mud can get into the suction basket. Use a coarser mesh on the suction basket (coarser = less clogging, but more dirt into the pump – you have to find a compromise according to the water quality).
Dug well with variable water level: A classic situation in villages. Place the suction basket at least 50 cm above the bottom of the well (not on the bottom – you would suck mud) and at least 30 cm below the minimum summer water level. With a fluctuating water level, consider a submersible pump instead of a suction pump.
Selection and installation of suitable couplings for the suction circuit
As I mentioned, joints are critical in the suction circuit. For garden installations with smaller flows (up to 50 l/min), brass threaded couplings are suitable, for larger flows, flanged couplings or thicker threaded nozzles are recommended. On the discharge side – where vacuum is not a problem – you can freely use practical GEKA bayonet couplings.
For the transition from the pump discharge to the garden irrigation, GEKA couplings with internal thread 1/2" are an ideal solution – the internal thread is directly screwed onto the external thread of the pump discharge and on the other side you connect the garden discharge. Similarly, GEKA coupling 1/2" with external thread allows you to connect to an internal thread valve or T-piece.
For more about different types of GEKA couplings and their comparison, you can read the article GEKA couplings vs. standard hose couplings – which are better and why directly in the Knowledge Center. Step-by-step installation is available in the article Installation of GEKA bayonet coupling on a hose or thread step by step.
Winterization of the suction pipe – prevention of frost damage
A suction hose full of water + frost = a burst hose or cracked fittings. Winterization of the suction circuit is a necessity, not an optional choice.
Procedure: After the season ends, drain the entire suction by opening the drain valve or by disconnecting the suction basket and letting the water flow out. If the suction hose has places where water stays (e.g. bends below the surface), blow compressed air into the hose from a compressor to push out the remaining water. Remove and clean the check valve and store it in a dry place – the rubber will harden and crack in the frost.
A more detailed procedure for preparing the entire garden irrigation for winter is available in the article Maintenance and winterization of garden irrigation, hoses and couplings in the Knowledge Center.
Most frequently asked questions (FAQ)
The pump ran perfectly all season, now after winter it doesn't suck – what happened?
The most common reason is a cracked check valve or its gasket due to frost. Pull out the suction basket, inspect the check valve – if the gasket or body is visibly cracked, replace it. Another possibility: the suction hose deformed in the frost and air is entering through microcracks in the material. Visually inspect the entire length of the hose and repeat the soap water test.
How many layers of PTFE tape are enough on a suction thread to be really tight?
Use at least 4–5 layers of PTFE tape on a suction thread, and that is wound in the direction of tightening (so that when tightening, the tape does not brush off, but winds up). For a larger thread 1" or 1¼", use also a thicker tape (1.2 mm instead of 0.1 mm) or a combination of tape and anaerobic sealant. After tightening, allow the anaerobic sealant at least 2 hours to cure before starting.
Can I use the same GEKA coupling on suction as on discharge?
Technically yes – GEKA couplings with bayonet seals are tight even under vacuum, if the rubber seal is in good condition. Practically, I do not recommend it where you will regularly open and close the coupling – every opening = air entering the suction system and need to prime. On the suction circuit, I recommend fixed joints (threaded or welded), use GEKA quick couplings on the discharge side, where they are much more practical.
The pump does suck, but the flow is much lower than the parameters – where is the problem?
The most common causes of reduced flow with otherwise functional suction: clogged suction basket (check and clean the mesh), too long or narrow suction (check the diameter), air in the suction (pulsations, bubbles), cavitation caused by exceeding the suction height, worn stator of the pump (after long-term use), or insufficient voltage in the electrical network causing a drop in motor speed.
Do I really have to place the suction basket 30 cm below the water level? What if the well is shallow?
Yes, 30 cm is the minimum in calm water. In a well where the water level fluctuates, or where there is movement (replenishment), use a larger distance – 50–60 cm. If the well is really shallow and this is not possible, you have to calculate with a level switch that turns off the pump before the water level drops below the suction basket. Otherwise, you risk dry running and rapid damage to the pump.
What is the difference between a 1" suction hose and a 1" rigid PP pipe in terms of functionality?
Both have the same inner diameter and therefore the same hydraulic behavior. A rigid PP pipe has zero risk of collapse, less friction resistance (smoother inner surface) and longer life – it is ideal for permanent installations. A spiral suction hose is flexible, easier to install in confined spaces or on uneven terrain, but has slightly higher friction resistance (grooves of the spiral reinforcement). For garden use, a flexible suction hose is more convenient, for permanent installations at a garden house or garage you choose a pipe.
Conclusion: reliable suction is the foundation of every garden water supply
The suction side of a pump installation is the technically most demanding element – and at the same time the one where the most improvisations and mistakes are made. Properly dimensioned diameter, minimal length and number of elbows, absolute tightness of each joint, functional check valve in the correct position, and regular maintenance of the suction basket – these are the pillars on which the reliability of every home water supply stands.
If you are not sure about the selection of the correct couplings for your specific diameter, I recommend looking at other articles in the Knowledge Center: What diameter hose and couplings do I need for my water pressure and garden and Suction hose for a home water supply – how to choose the correct diameter and length. These topics are interrelated and together form a complete guide to a problem-free garden water supply for the entire season.