A Pulsometer Steam Pump is a valveless, pistonless reciprocating pump that lifts water by alternately admitting steam to two chambers and condensing it against the cold water surface to draw the next charge in. The Hall Pulsometer used widely on Victorian railway construction sites is the classic example. It exists to dewater pits, mines and trenches where mud and grit would chew up a piston pump in days. A modest unit handles 50–500 gpm against 30–80 ft head with only ball check valves to wear out.
Pulsometer Steam Pump Interactive Calculator
Vary chamber volume, cycle rate, volumetric efficiency, and head to estimate pulsometer pump delivery and hydraulic output.
Equation Used
The pulsometer delivery estimate multiplies one chamber working volume by distributor cycles per minute, then by two chambers and volumetric efficiency. The head input is used only to estimate hydraulic water horsepower.
- Both chambers discharge once per distributor cycle.
- Volumetric efficiency represents incomplete filling, leakage, and condensation losses.
- Hydraulic horsepower uses water flow and total delivery head only.
The Pulsometer Steam Pump in Action
The Pulsometer is a direct descendant of the Savery engine, and it works on the same trick — condense steam to make a vacuum, push water with fresh steam, repeat. Two cast-iron chambers sit side by side under a top casting that holds a single rocking ball distributor. Live steam enters whichever chamber the ball uncovers. The hot steam pushes the standing column of water down and out through the lower ball check, up the delivery pipe. As the chamber empties, the steam touches the cold incoming water at the suction inlet and condenses almost instantly, dropping pressure inside the chamber to roughly 2–3 psia. Atmospheric pressure on the suction sump then pushes a fresh charge of water up through the foot valve and the suction ball check. The distributor ball rocks across to the other side under the imbalance, and the cycle repeats on the second chamber, typically at 40–80 cycles per minute.
There are no pistons, no glands, no crankshaft, no eccentrics. The only moving parts are the two ball check valves at the bottom of each chamber, the two delivery balls, and the rocking distributor ball on top — five balls total in a Hall pulsometer. That is why contractors loved it on muddy work. Grit just rolls past a 75 mm rubber-faced ball valve where it would score a piston ring in a day.
The design fails in three predictable ways. If the suction lift exceeds about 25 ft of water, the vacuum side cannot pull a charge fast enough and the unit short-cycles, blowing live steam straight out the delivery. If the feedwater is already hot — above roughly 40 °C — the steam will not condense fully and you lose vacuum, again causing short-cycling. And if the distributor ball seat wears oval (the common long-term failure), steam blows past into the wrong chamber and the pump goes silent with both chambers full. The cure is reseating the ball with a hand scraper to a 0.05 mm contact band — not lapping it round, which destroys the snap-action.
Key Components
- Twin Condensing Chambers: Two pear-shaped cast-iron chambers, typically 200–600 mm diameter, where steam alternately drives water out and condenses to draw water in. Wall thickness runs 12–18 mm to handle 60–100 psig live steam plus the thermal cycling between roughly 150 °C and 30 °C every second.
- Distributor Ball: A single bronze or rubber-coated ball, 50–100 mm diameter, that rocks between two seats in the top casting to admit steam to whichever chamber just finished its delivery stroke. Seat contact band must stay under 0.05 mm wide or the ball loses snap-action and steam leaks across.
- Suction Ball Check Valves: One per chamber, sitting at the bottom of the casing. They open inward on the vacuum stroke to admit a fresh charge of water from the suction sump and slam shut when steam pressure rebuilds. Ball lift is limited to about 1/4 of ball diameter to keep cycle time short.
- Delivery Ball Check Valves: One per chamber on the discharge side. They open outward when steam pressure exceeds delivery head and prevent backflow during the vacuum stroke. Brass or rubber-faced ball, sized so terminal velocity in water stays below 2 m/s to avoid hammer.
- Air Vessel: A small dome on the delivery line that absorbs the pressure pulse from each chamber discharge so the delivery pipe sees a steady flow rather than violent slugs. Sized at roughly 3–5× the volume of one chamber discharge.
- Steam Inlet and Throttle: Single 25–50 mm gate or globe valve admitting saturated steam at 60–100 psig. Throttling this valve is the only speed control the operator has — closing it slows the cycle rate but also drops delivery head.
Who Uses the Pulsometer Steam Pump
The Pulsometer found its niche wherever the water was dirty, the site was temporary, and a steam supply was already on hand. Because the only wear parts are five balls, contractors could leave a pulsometer running 24 hours a day in a flooded foundation pit and replace a worn ball in 10 minutes without pulling the unit out of the sump. That is a ratio of uptime-to-maintenance no piston pump of the era could match.
- Civil Construction: Hall Pulsometer pumps used on the construction of the London Underground District Line cut-and-cover works in the 1860s to dewater the trenches between the Royal Engineers' steam boilers and the running tunnels.
- Mining: Cornish tin and copper mines used pulsometers as standby pumps below the main Cornish beam engines, particularly at South Crofty mine where pulsometers handled the upper-level adit drainage.
- Quarrying: Penrhyn slate quarry in North Wales ran pulsometers in the working faces to dewater drilling chambers, fed off the same boiler that powered the inclined-plane haulage.
- Marine Salvage: Royal Navy salvage tenders carried pulsometers as portable dewatering pumps for grounded vessels through to the 1920s, since they could swallow sand and silt without complaint.
- Heritage Steam: The Kew Bridge Steam Museum in west London demonstrates a working Hall pulsometer alongside the Cornish engines, lifting water from a sump back to the header tank for the visiting public.
- Sugar Mills: West Indies sugar estates used pulsometers to lift cane juice and condensate from sub-floor catch tanks, taking process steam directly off the evaporator manifold.
The Formula Behind the Pulsometer Steam Pump
The practical question with a pulsometer is always: how much water will it deliver per minute against my actual head? Output depends on chamber volume, cycle rate and a volumetric efficiency that drops sharply at the edges of the operating range. At the low end of typical cycle rate (around 30 cpm) the chambers fully fill and discharge but you get fewer cycles per minute. At the high end (around 90 cpm) the cycles are quick but the chambers do not fully fill on the vacuum stroke and volumetric efficiency falls to roughly 0.55. The sweet spot sits at 50–70 cpm where ηv holds at about 0.75 and total delivery is highest.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| Q | Delivered water flow rate | m³/min | gpm |
| Vc | Working volume of one chamber per stroke | m³ | gallons |
| N | Cycle rate of the distributor ball | cycles/min | cycles/min |
| ηv | Volumetric efficiency (fraction of chamber actually filled and discharged) | dimensionless | dimensionless |
| 2 | Factor for the two chambers — each fires once per full cycle of the distributor | — | — |
Worked Example: Pulsometer Steam Pump in a heritage brickworks clay-pit dewatering set
Sizing the delivery rate from a recommissioned 1894 Hall No. 6 Pulsometer being returned to working duty at a heritage clay-pit dewatering demonstration at the Bursledon Brickworks Industrial Museum in Hampshire, where the trustees want to lift seepage water out of a 22 ft deep clay pit back up to the surface settling pond, fed from the museum's restored Cornish boiler at 75 psig saturated steam. Each chamber on a Hall No. 6 measures roughly 0.018 m³ working volume, and the distributor naturally cycles in the 50–70 cpm range at this steam pressure.
Given
- Vc = 0.018 m³
- Nnom = 60 cycles/min
- ηv,nom = 0.75 —
- Steam supply = 75 psig saturated
- Suction lift = 22 ft
Solution
Step 1 — compute nominal delivery at 60 cpm with a healthy 0.75 volumetric efficiency, which is what a properly seated Hall No. 6 returns when feedwater is below 30 °C:
That converts to roughly 356 imperial gpm. For a 22 ft suction lift this is well within the pulsometer's comfort zone — it will keep up with seepage in a clay pit of that size without short-cycling.
Step 2 — at the low end of typical operating range, the operator throttles the steam supply to slow the unit to 35 cpm. Volumetric efficiency actually rises slightly because the chambers have more time to fill:
Around 227 gpm. You would use this setting overnight when seepage is light and you want to stretch coal in the boiler. The pump runs visibly slow — you can count the chamber bumps by ear.
Step 3 — at the high end, opening the steam valve fully drives the cycle to 85 cpm but volumetric efficiency collapses because the chambers do not fully fill on the vacuum stroke:
Roughly 389 gpm — only about 10% above nominal despite running 40% faster, and the unit is now swallowing far more steam per gallon delivered. Above 85 cpm the suction starts to whistle as the foot valve cavitates, and you waste boiler output for almost no extra water.
Result
Nominal delivery from the recommissioned Hall No. 6 at 60 cpm comes in at 1.62 m³/min, or about 356 gpm. That is plenty to keep a 22 ft clay pit dry against typical seepage, with steam consumption running roughly 180 lb/h off the Cornish boiler. The range tells you the sweet spot sits firmly at 50–70 cpm — pushing to 85 cpm only buys you 10% more water for 40% more steam, and the foot valve cavitates audibly. If your measured delivery falls 30% below the predicted 1.62 m³/min, the three usual suspects are: a worn delivery ball seat letting water slip back during the vacuum stroke (look for a ring of bright metal on the seat), feedwater above 40 °C entering the chambers and ruining condensation (check sump temperature), or the air vessel waterlogged so the delivery pipe is fighting hammer instead of steady flow (crack the pet-cock on top of the dome and listen for air).
Choosing the Pulsometer Steam Pump: Pros and Cons
The Pulsometer competes with two other dirty-water pump families a Victorian or heritage-site engineer would consider — the direct-acting Worthington duplex steam pump and the centrifugal pump driven off a small steam turbine or engine. Each has a clear operating window.
| Property | Pulsometer Steam Pump | Worthington Duplex Steam Pump | Steam-driven Centrifugal Pump |
|---|---|---|---|
| Typical flow range | 50–500 gpm | 20–2000 gpm | 200–10,000 gpm |
| Maximum suction lift | 22–25 ft | 20 ft | 20 ft (limited by NPSH) |
| Maximum delivery head | 80–120 ft | 300+ ft | 150–400 ft |
| Tolerance for grit and mud | Excellent — only 5 balls in flow path | Poor — wears piston rings and rod packing fast | Moderate — abrasive wear on impeller vanes |
| Steam consumption per gallon delivered | High — roughly 0.5 lb steam/gal | Moderate — 0.15 lb steam/gal at best duty | Moderate — depends on prime mover efficiency |
| Wear parts to replace | 5 balls and seats | Pistons, rods, packings, valves, eccentrics | Impeller, wear rings, mechanical seal |
| Field maintenance interval | 3–6 months continuous duty | Weekly packing checks, monthly valve work | 6–12 months on clean water |
| Best application fit | Dirty temporary dewatering, contractor pits | Boiler feed and clean-water duties at high head | Large-volume drainage and circulation |
Frequently Asked Questions About Pulsometer Steam Pump
Classic symptom of a flooded distributor — the rocking ball on top has either lost its snap-action or the chambers have over-filled on the vacuum stroke. Most often the cause is a slug of cold water carried up into the steam dome by violent condensation, which kills the steam pressure differential the ball needs to rock across.
The fix is to close the steam valve, crack the drain cocks at the bottom of both chambers, and bleed the water down to the foot-valve level. Then re-open steam slowly. If it happens repeatedly, your steam supply line is too long and unlagged, so steam is condensing in the pipe before it reaches the pump. Lag the supply line and add a steam trap immediately upstream of the pump.
Strictly dewatering and process-water lifting. The steam consumption is brutal — roughly 0.5 lb of steam per gallon delivered, which is 3 to 4 times what a Worthington duplex pump uses for the same duty. Feeding a boiler with a pulsometer means you spend a third of your boiler output just pumping its own feedwater, which is an obvious losing game.
Use a pulsometer where steam is effectively free (you have spare boiler capacity sitting idle anyway), the water is dirty, and the duty is intermittent. Mine sumps, foundation pits, and quarry dewatering are the correct applications. Boiler feed, condensate return, and any closed-loop service should go to an injector or a piston pump.
The pump runs on condensation, not displacement alone. Each cycle relies on the cold incoming water charge condensing the steam in the chamber, which is what creates the vacuum that draws the next charge. Above roughly 40 °C the steam will not fully condense — the residual vapour pressure props up the chamber pressure and you lose most of your suction stroke.
This is the single most under-appreciated limit on pulsometer operation. If your sump runs warm, you have two options: pipe in a cold-water bleed at the suction inlet to drop the mixed temperature, or accept that summer output will be 30–50% of winter output. There is no way to tune around it — it is set by the saturation curve of water.
Working volume is roughly 60% of the geometric chamber volume on a Hall pattern, because the upper portion of each chamber must remain a steam space for the live steam to push against. The clearance volume above the working water level is typically 35–40% of total internal volume.
Quick rule of thumb for Hall pumps: a No. 4 gives about 0.010 m³ working, a No. 6 gives 0.018 m³, a No. 8 gives 0.030 m³, and a No. 10 gives 0.045 m³. If you are working from drawings, take 0.6 × the geometric internal volume of one chamber and you will be within 5% of true.
Your air vessel has waterlogged. The dome on the delivery line is supposed to hold a trapped air cushion that absorbs the pulse from each chamber discharge. Over hours of running, that air dissolves into the water and gets carried away, leaving the dome full of water and offering zero damping.
Stop the pump, open the pet-cock at the top of the dome, and let it drain back to roughly half full. Re-start. If it waterlogs again within an hour you need a snifter valve fitted to the suction side that admits a small charge of air on each vacuum stroke — that was the standard Hall fix and most original installations had one. Without it, the hammer will eventually crack the delivery pipe at the first rigid joint.
You can but you will damage the distributor ball and seats within hours. Pulsometers are designed for saturated steam — the cycle relies on the steam condensing rapidly when it touches the water charge. Superheated steam takes longer to give up its heat, which extends the discharge stroke and lets the steam temperature rise on the seats well above the 150 °C they are designed for.
A rubber-faced distributor ball will harden and crack inside a shift on superheated supply. If superheated steam is all you have, fit a desuperheater (a simple water-injection nozzle) on the supply line to drop the steam back to roughly 5–10 °C above saturation before it enters the pump. The flow drops slightly but the pump survives.
References & Further Reading
- Wikipedia contributors. Pulsometer steam pump. Wikipedia
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