Silty Trench Dewatering Pump Kit | EVAK Trenchman 400
Silty trench dewatering pump kit for muddy water, fines and settled silt This FPS Engineered™ kit pairs the EVAK Trenchman 400 with 20m of 50mm layflat hose and a stainless-steel clip. The Trenchman has a built-in agitator, which is what separates it from every other pump in our site range. Part of our wider site drainage and EVAK ranges. Why a pump alone cannot clear silty water A pump can only move what is in suspension. Once silt, sand and fines have settled out, they behave less like water and more like ground. A standard drainage pump sitting on top of that layer will happily draw the clearer water above it and discharge that instead, hour after hour, while the sludge stays exactly where it is. You end up with a trench that looks pumped and is still full of material. The Trenchman has an agitator at the intake: a rotating element that disturbs settled material and lifts it back into the water so the pump can carry it away. Free passage of 15mm then gives that material somewhere to go, where a 5mm pump would simply block. The result is that you remove the silt rather than the water sitting on top of it, which is usually the whole point of dewatering a trench in the first place. At a glance Built-in agitator: Stirs settled silt and fines back into suspension so they can be pumped out. 15mm free passage: Three times the Drainox, so fines, grit and small stones pass rather than block. Around 189 litres per minute: Through the 20m of layflat supplied, at a typical 2m lift. 12 metres of head: Still moving 119 litres per minute at an 8m lift. Automatic float control: Left in the trench, it works while you get on with something else. What's included 1 × EVAK Trenchman 400 submersible trench pump with agitator 1 × 20m length of 50mm layflat hose 1 × 40 to 60mm stainless-steel hose clip When not to use an agitator pump An agitator is a specialist tool. Where sediment has settled and you would rather it stayed put, stirring it up is the wrong move. In a permanent sump, a clean water chamber or a tank you are emptying for reuse, suspending the silt means pumping abrasive material through the pump and depositing it wherever the hose discharges. If the water is reasonably clear and the silt is best left alone, the Drainox site drainage kit is the better choice. Use the Trenchman where the material genuinely has to come out. Expected performance Estimated flow through the supplied 20m of 50mm layflat, discharging freely. Lift is measured from the water surface to the point where the hose discharges. Uphill lift Typical situation Estimated flow Per hour 2 m Shallow trench, ground level discharge Approx. 189 L/min Approx. 11,300 litres 4 m Trench up to a kerb or gully Approx. 169 L/min Approx. 10,100 litres 6 m Deep trench or excavation Approx. 146 L/min Approx. 8,800 litres 8 m Deep dig with a high discharge point Approx. 119 L/min Approx. 7,100 litres 10 m Approaching the pump's limit Approx. 84 L/min Approx. 5,000 litres Estimated using the published Trenchman 400 curve and Hazen-Williams friction for 50 mm bore, for water only. Friction across the full 20 m run is under 1 m of head. Solids in suspension increase the density of what the pump is moving, so heavily silted water will flow more slowly than these figures suggest. Work out a specific run with our pump performance calculator. Technical specification Specification EVAK Trenchman 400 Operation Automatic, float switch Pump type Submersible trench pump with agitator Maximum flow 220 litres per minute Maximum head 12 metres Free passage 15 mm Agitator Built in, at the intake Discharge 50 mm, 2 inch Voltage 230 V single phase How it fits the EVAK range EVAK make three site pumps that look similar and do different jobs. Free passage is what separates them, and choosing on flow alone is how people end up with the wrong one. Pump Free passage Choose it when Residox 2 mm You need a floor taken back to near-dry. A residue pump, not a site pump. Drainox 5 mm The water is reasonably clear, and any sediment is best left where it is. Trenchman 15 mm, with agitator The silt has to come out, not just the water sitting on top of it. A larger Trenchman 750 is also available, at 350 litres per minute and 18 metres of head, for deeper digs and sustained groundwater. Using it in a trench Set the pump on the firmest part of the base you can find, so the agitator works on the material rather than burying itself in it. Keep the float clear of the trench wall and of any suspended debris. In silty water a float can foul, so check it is swinging freely. Discharge somewhere the silt can settle out. Sediment-laden water should not go to a watercourse or a surface water drain, and it will silt up whatever it runs into. Keep the plug and connections dry and above any possible water level, and never lift the pump by its cable. Flush the pump and hose through with clean water at the end of the job. Abrasive material left inside is what wears a pump out. What can I use it for? Trench dewatering in groundworks, drainage and utilities work Excavations and footings where the base has turned to slurry Clearing silt traps, settlement tanks and interceptors Pumping out ponds, lagoons and attenuation tanks with a settled bottom Cleaning out chambers, manholes and sumps that have silted up Wash-down and slurry water on farms and yards Water quality limits Silty and dirty water, solids to 15 mm. The Trenchman is built to tolerate abrasive material far better than a clean-water pump, but nothing pumps sand indefinitely without wear. Flush it through after every job. It is not a sewage or solids-handling pump, and not for foul water or salt water. Frequently asked questions What does the agitator actually do? It stirs settled silt, sand and fines back into the water so the pump can carry them away. Without one, a pump sitting on a bed of silt draws the clearer water above it and leaves the material behind, so the trench never really empties. How is this different from the Drainox site drainage kit? Free passage and the agitator. The Drainox passes 5 mm and is the right pump where the water is reasonably clear. The Trenchman passes 15 mm and actively lifts settled material into suspension. If the bottom of your trench has gone to slurry, only one of them will clear it. Should I use it if the water is clean? Usually not. Stirring up sediment that would otherwise stay put means pumping abrasive material through the pump and depositing it at the discharge. Where the silt is best left alone, use a Drainox. Will it pump thick mud? It handles silty, muddy water with solids up to 15 mm, but it is a water pump with an agitator, not a slurry pump. If the material will not flow, it needs excavating rather than pumping. Why is there no choice of hose length? Because at 50 mm bore it would not change anything. Doubling from 10 m to 20 m costs around 3 percent of the flow, which is smaller than the margin of error on the estimate, so we supply the longer one. Do the published flow figures apply to silty water? They are calculated for water. Solids in suspension make what the pump is moving denser and heavier, so heavily silted water will flow more slowly. Treat the figures as the clean-water ceiling. Is a larger version available? Yes, the Trenchman 750 at 350 litres per minute and 18 metres of head, for deeper digs and sustained groundwater.