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How to Choose a Pump for Dirty Water

Trash pumps are essential for getting rid of dirty water. Whether you need to drain a pond of muddy water or clean out a flooded basement, you will need a special pump designed to move water containing solids and sediment. These trash pumps are designed to handle mixed solids and liquids without failing or clogging.

There are various pump designs available on the market. However, most of them are designed specifically for clean water, like pool pumps or garden pumps, while only specialised pumps can handle contamination, which we will discuss in this article. These are typically either open-impeller centrifugal pumps or diaphragm pumps. Understanding which type of pump you need is the first step to making the right choice.

We will go over the complexities of choosing a dirty water pump. We will discuss the different types of pumps, factors to consider when buying one, and the best methods of using the pump. By the end of this guide, you will fully understand how to choose a dirty water pump.

How to choose a Pump for Dirty Water

Table of Contents:

How dirty is your water?

Pumping water containing solids and sediment is a complex task that requires a pump designed specifically for this purpose. Unlike clean water, dirty water contains varying proportions of sediment and debris that can clog a standard pump and render it unusable. When assessing pump requirements, three things should be evaluated:

  • maximum size (diameter) of solid particles in millimetres,

  • the proportion of solids in water in grams per 1 cubic metre,

  • the density of suspended inclusions (mud, sludge, slurry, presence of fibrous inclusions, etc.).

The particle size is determined by the opening on the outer filter of the suction hose through which the unit draws water. This strainer prevents large debris from entering and clogging the pump, thus ensuring efficient pump operation. The size of the mesh on the filter is, therefore, an indirect parameter by which you can understand what kind of water the pump is designed for:

Solid Sizes RA Foeas Water Pumps
Solid Sizes

  • Impurities up to 9 mm. The device will cope with lightly contaminated water from a swimming pool, irrigation cistern or other reservoir with a small content of solid objects. This pump is also suitable for irrigation from natural water bodies (ponds, lakes, canals) including small twigs and leaves.

  • Impurities up to 20 mm. The pump will be able to drain a flooded cellar or a construction pit (for foundations). This is the type of pump used for flooding and dewatering of water bodies.

  • Impurities up to 50 mm. The unit is suitable for pumping melt water, rain water, waste water from pits and ditches. In fact, this type of pump is an all-terrain vehicle in the world of drainage pumps.

A summary of common levels of water dirtiness and which pump to use:

Clean water

Ponds, lakes, canals

Flood water

Sludge, liquid food, bildge

Particle size

<1 mm

1-9 mm

9-20 mm

20-50 mm

Pump required

Water pump

Semi-trash pump

Trash pump

Diaphragm pump

⚠️Caution: When handling sandy water, it is important to ensure that sand does not build up in the pump. This can be achieved by cleaning the pump regularly and ensuring that the sand is effectively removed from the water before it enters the pump.

As the water becomes dirtier, so do the engineering specifications of the pumps. Trash pumps have a specially designed casing and open impeller to handle the sediment and pebbles in the muddy water. The pump housing is often made of durable material, such as stainless steel or cast iron, to withstand the erosive wear and tear of pumping dirty water. The impeller, in turn, has larger blades made from wear-resistant materials such as cast iron with high chromium content. This allows it to crumble and move small debris with the water without clogging.

🔥 Trash pumps are generally not designed for pumping hot water; domestic models are designed for a maximum operating temperature of 35-40 °C. The ability to pump hot water is stated in the instructions.

Types Trash Pump for Dirty Water

Open impeller centrifugal pumps are the most common pumps available for pumping dirty water. They have a simple design as they use centrifugal force for the simultaneous movement of large volumes combined with high pressure resulting in a high head (height). They allow the pumping of large volumes of dirty water in a short time. Builders often use such pumps on construction sites for draining pits and trenches.

These pumps are indispensable in emergency cases of flooding. In industry, centrifugal pumps with open impellers are used for pumping corrosive liquids with impurities of abrasive materials - sand, stone chips, cement and other inclusions of solid particles, where high flow speed is required. Larger blades in the impeller allow the pump to handle larger debris and prevent clogging. Thus, centrifugal pumps with open impellers are designed for pumping liquids containing suspended soft and solid particles, except fibrous material (strings or hairs). Impeller centrifugal pumps have a simple design, which gives them versatility in application, simplifies operation and maintenance, and favourably affects the cost of the equipment.

Electric centrifugal trash pumps - RA series

Foras Ra-series

The size of the pump and its capacity must be considered. Larger pumps can pump more water but may be more difficult to operate and maintain. On the other hand, smaller pumps may be easier to handle but may not be able to handle the task of pumping dirty water.

Standard household pumps are single however when needed pumps also come in three-phase versions identified with "T" symbol:

Depending on how long you need your pump to last pumps the RA series pumps come with a brass impeller instead of a Noryl impeller signified by "/1" in the product description. These pumps last longer having a more durable impeller:

We also have spare parts available for all the RA series Foras pumps (which are also CR series Pentax pumps) for example here for RA82:

Gasoline Trash and Semi-Trash Pumps

Koshin Ltd., a world-renowned leader in the manufacturing of water pumps, offers a diverse range of gasoline trash and semi-trash pumps, powered by Honda engines. These pumps are known for their high performance, durability, and dependability, making them a top choice for various applications.

Types of Koshin Gasoline Trash and Semi-trash Pumps

Types of Koshin Gasoline Trash and Semi-trash Pumps

Several types of Koshin gasoline trash and semi-trash pumps are designed to handle different kinds of debris-laden water. The main difference among them is the size and type of debris they can handle.

  1. Trash Pumps: These pumps are designed for handling water containing large solids and debris. Their impellers are typically designed with wide passages to prevent clogging.

  2. Semi-trash Pumps: These are designed for water containing smaller solids and debris. They are not designed to handle large debris like their trash pump counterparts.

Variations in gasoline pumps based on size

The variations in Koshin pumps are not limited to the type of debris they handle. They also vary based on size, which typically ranges from 2 inches to 4 inches.

  1. 2-Inch Koshin Pumps: These are compact, lightweight pumps, making them ideal for residential and light commercial applications. Despite their size, they offer remarkable power and efficiency, capable of moving up to 158 gallons of water per minute.

  2. 3-Inch Koshin Pumps: Offering a balance between power and portability, 3-inch pumps are suitable for more demanding applications. They can typically handle larger volumes of water and more substantial debris, making them ideal for construction, agricultural, and industrial applications.

  3. 4-Inch Koshin Pumps: These are the most powerful and robust pumps in the range. Capable of moving up to 555 gallons per minute, they are designed for heavy-duty applications where high water flow is required. These are most commonly used in construction sites, large-scale agricultural operations, and flood recovery situations.

Diaphram pumps - Ecologically friendly

Diaphragm pumps are a less common type of pump and they work by bending a diaphragm in the pump chamber, creating a vacuum that draws dirty water into the pump. These pumps are reliable and can handle significant debris without clogging. In addition, they are environmentally friendly to the fauna and flora contained in the water. Thus, they are able to pump without damaging algae, eggs and fry from the pond. Another advantage is the ability to pump viscous liquids: water with increased sand and mud, sludge and waste from cesspools. The disadvantage of diaphragm pumps is low pressure/head and flow rate.

This pump is ideal for applications where the water is not too dirty and high flow rates are not required. Its main advantages are the ability to operate without damaging the bio-organisms in the water and the high content of fibrous impurities and sludge.

Diaphragm pumps Caffini

Which criteria to consider when selecting a pump?

Pump power performance is the main information when evaluating different models of dirty water pumps.

How much water and how high?

  • Flow rate: For domestic use a pump with a flow rate of 5-10 cubic metres per hour is sufficient For irrigation of a small garden plot in particular, 0.4-0.6 cubic metres per hour is sufficient. For construction and industrial needs, the pump capacity should be calculated with the help of engineering computer programmes or by relying on the professional experience of end users.

  • Pressure: The pressure or head helps you understand how far you can lift and pump water. It is generally assumed in rough calculations that 1 metre of vertical head roughly corresponds to 10 metres of horizontal pumping, so it is useful to assess the conditions of use and distances in advance.

How If you are comparing models in terms of performance, also consider the time it will take to complete a task and focus on the most demanding task. For long-lasting operation of the pump, the above-mentioned parameters should be set between 55-85 % of the system's maximum capacity.

Which manufactuer?

The choice of manufacturer is usually based on the budget and personal preferences of the buyer. The models of well-known European manufacturers will ensure future reliable operation, maintainability and warranty obligations. Choosing a cheap model with a significantly lower price may lead to dissatisfaction with the declared technical characteristics, early breakdowns and a complete lack of service and spare parts.

Does the pump need to suck water from below?

When selecting a pump, you should consider the possibility of suction if you plan to pump water below the installation level. Firstly, not all models are self-priming and secondly, all pump can only have a maximum depth of 9 metres due to Torricelli's principle. In reality, a stable suction depth of no more than 5 metres should be assumed.

If the depth is greater than this, submersible pumps should be used to push the water upwards instead of sucking the water up. The submersible pump for dirty water is a reliable and powerful pump capable of handling high concentrations of solids and sludge. It is designed to be submerged in water and can pump a large volume of water at a time. These pumps are ideal for draining ponds or handling water with high sediment content. Its main advantages are the much greater depth of the lower water level and the low noise level. See our blog, and a common list of submersible pump products:

How long will my trash pump last?

Material. Sometimes water contains active impurities (chemicals). Manufacturers usually take into account the possibility of use in such conditions and use materials resistant to aggressive environment and corrosion. Stainless steel or particularly durable plastic is chosen for the housing. Under normal conditions, the materials behave almost identically, but in aggressive environments stainless steel is preferable and such a pump will cost more.

Protection class. One of the characteristics is the degree of protection, which is expressed in an international classification, e.g. labelled IP55 or IPX5. This parameter in the description of the pump characterises the safety of the pump against mechanical particles and water penetration.

Availability of protections. It is important to remember that running without water, dry, even for a few minutes, can ruin any pumping equipment. At a minimum, the motor shaft seal will be overheated and the Teflon rings will crack when water enters. To protect against dry running, drainage pumps are equipped with sophisticated electronic protection devices or float switches.

It is an important and reliable element for automating and protecting the mechanism against deterioration. The float switch has two operating modes:

  • When there is a lot of water, at this point, the mechanism is switched on (contacts are closed), and the pump continues to function.

  • When the level drops to the critical level, the float is lowered, the contact opens (a steel ball is used for this purpose), and the motor stops.

In addition, most modern dirty water pumps are equipped with additional automatic protection options, such as a thermal relay. This stops operation if the motor overheats and restarts it when it cools down again.

Conclusion: Purchasing the right pump for your needs

Choosing the right dirty water pump is critical to ensuring that your pond, basement, or anywhere else your water and debris are handled efficiently. Knowing the different types of pumps, factors to consider when selecting a pump, and how to operate and maintain the pump will help you make the right purchase for your needs.

Remember that choosing the best pump depends on your specific needs. Consider the type of water you will be pumping, the volume of water you need to pump and your budget to make sure you choose the right pump.

Ready to buy? See our selection of electric trash pumps or our selection of gasoline semi-trash pumps. We offer a wide range of pumps to meet your every need. Whether you need a submersible dirty water pump, drainage pump, or diaphragm pump, we're here to help. Don't let dirty water get in your way. Buy a pump today and operate it like a pro.


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