Slurry Pump Sealing System; What Happens If It Runs Dry?
Your Pump Questions Answered: As specialists in quarry water management, we often get interesting questions regarding slurry pumping and abrasive fluids handling. By sharing these questions and answers we hope they will be useful for others looking for similar advice.
A question asked by a user in Peru, after reading the Slurry Pump troubleshooting checklist:
“What Happens To The Seal Water System In A Slurry Pump When The Feedbox Runs Out Of Load (Slurry)”
This question regards the gland package assembly, also known as a Stuffing Box, in a wet seal system of a slurry pump. The purpose of this 'packed gland seal' is two-fold; firstly it stops excessive leaking from the pump by closing the gap between the shaft and the fixed casing. Secondly, it lubricates the spinning shaft and helps keep it from overheating. The seal consists of rope which has liquid seeping through it, dissipating the heat and reducing friction.
There are two types of packed gland seal, the most basic one uses the fluid being pumped as the lubrication and cooling agent, whereas the flushed gland seal uses a secondary pump and a clean water supply. The former leaks a little, whilst the latter dilutes a little.
So, if the seal is allowed to dry out whilst the pump is still running it is likely to generate friction between the spinning shaft and seal, possibly even resulting in friction wear of the stationary casing of the volute wall. This friction will cause the wearing of the parts and generate heat, which means wasted energy and the need for pump disassembly, replacement of worn parts and repacking of the burned seal.
Even where the pump is switched off whilst dry, upon re-supply of the slurry you may experience a short period of increased leakage as the seal re-wets itself.
Of course, where a flushed seal gland is used, the gland shouldn't dry out when the slurry feed stops. However, the clean water consumption and its associated costs will increase due to the lack of pressure within the inside of the pump's casing.
How Can Dry Seals Be Prevented?
Only have your pump running if there is sufficient fluid being supplied. It is better to allow the feed to fill up before starting the pump in order to reduce the number of starts, which will reduce energy costs and put less wear and tear on your pump. Also, turning your pump off before it runs dry has the following advantages:
1) You are less likely to need to re-prime the pump next time you start it.
2) The seals will remain wet for longer.
3) It reduces the risk of cavitation damage (which occurs when the in-feed pressure is too low)
Note; If your slurry is likely to set or harden if left for a period of time, flush out the system with water before leaving it turned off.
Alternatives To Wet Sealing Systems:
Expeller Seals and Mechanical Seals are higher performing alternatives to traditional gland packing seals. The standard seals used by heavy-duty slurry pump manufacturer SlurryPro are expeller type seals, as these have higher performance and reduced maintenance needs. For environments or liquids that require leakage-free pumping, the ultimate shaft sealing system is a precision mechanical seal. These are made to such precise tolerance as to negate the need for gland seal packing, vastly reducing maintenance costs and being ideal for when no leakage is acceptable.
For More On Slurry Pump Troubleshooting Problems See Our Troubleshooter For Slurry Pumps
Changing the Gland Packing in an Expeller Seal
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